Secara harfiah, internet (kependekan dari interconnected-networking) ialah rangkaian komputer yang terhubung di dalam beberapa rangkaian. Manakala Internet (huruf 'I' besar) ialah sistem komputer umum, yang berhubung secara global dan menggunakan TCP/IP sebagai protokol pertukaran paket (packet switching communication protocol). Rangkaian internet yang terbesar dinamakan Internet. Cara menghubungkan rangkaian dengan kaedah ini dinamakan internetworking.
Daftar isi [sembunyikan]
1 Kemunculan Internet
2 Internet pada saat ini
3 Budaya Internet
4 Tata tertib Internet
5 Isu moral dan undang-undang
6 Akses Internet
7 Penggunaan Internet di tempat umum
8 Tokoh-tokoh Internet
9 Lihat pula
10 Pranala luar
[sunting] Kemunculan Internet
Rangkaian pusat yang membentuk Internet diawali pada tahun 1969 sebagai ARPANET, yang dibangun oleh ARPA (United States Department of Defense Advanced Research Projects Agency). Beberapa penyelidikan awal yang disumbang oleh ARPANET termasuk kaedah rangkaian tanpa-pusat (decentralised network), teori queueing, dan kaedah pertukaran paket (packet switching).
Pada 1 Januari 1983, ARPANET menukar protokol rangkaian pusatnya, dari NCP ke TCP/IP. Ini merupakan awal dari Internet yang kita kenal hari ini.
Pada sekitar 1990-an, Internet telah berkembang dan menyambungkan kebanyakan pengguna jaringan-jaringan komputer yang ada.
[sunting] Internet pada saat ini
Representasi grafis dari jaringan WWW (hanya 0.0001% saja)Internet dijaga oleh perjanjian bi- atau multilateral dan spesifikasi teknikal (protokol yang menerangkan tentang perpindahan data antara rangkaian). Protokol-protokol ini dibentuk berdasarkan perbincangan Internet Engineering Task Force (IETF), yang terbuka kepada umum. Badan ini mengeluarkan dokumen yang dikenali sebagai RFC (Request for Comments). Sebagian dari RFC dijadikan Standar Internet (Internet Standard), oleh Badan Arsitektur Internet (Internet Architecture Board - IAB). Protokol-protokol internet yang sering digunakan adalah seperti, IP, TCP, UDP, DNS, PPP, SLIP, ICMP, POP3, IMAP, SMTP, HTTP, HTTPS, SSH, Telnet, FTP, LDAP, dan SSL.
Beberapa layanan populer di internet yang menggunakan protokol di atas, ialah email/surat elektronik, Usenet, Newsgroup, berbagi berkas (File Sharing), WWW (World Wide Web), Gopher, akses sesi (Session Access), WAIS, finger, IRC, MUD, dan MUSH. Di antara semua ini, email/surat elektronik dan World Wide Web lebih kerap digunakan, dan lebih banyak servis yang dibangun berdasarkannya, seperti milis (Mailing List) dan Weblog. Internet memungkinkan adanya servis terkini (Real-time service), seperti web radio, dan webcast, yang dapat diakses di seluruh dunia. Selain itu melalui internet dimungkinkan untuk berkomunikasi secara langsung antara dua pengguna atau lebih melalui program pengirim pesan instan seperti Camfrog, Pidgin (Gaim), Trilian, Kopete, Yahoo! Messenger, MSN Messenger dan Windows Live Messenger.
Beberapa servis Internet populer yang berdasarkan sistem tertutup (Proprietary System), adalah seperti IRC, ICQ, AIM, CDDB, dan Gnutella.
[sunting] Budaya Internet
Jumlah pengguna Internet yang besar dan semakin berkembang, telah mewujudkan budaya internet. Internet juga mempunyai pengaruh yang besar atas ilmu, dan pandangan dunia. Dengan hanya berpandukan mesin pencari seperti Google, pengguna di seluruh dunia mempunyai akses internet yang mudah atas bermacam-macam informasi. Dibanding dengan buku dan perpustakaan, Internet melambangkan penyebaran(decentralization) / pengetahuan (knowledge) informasi dan data secara ekstrim.
Perkembangan Internet juga telah mempengaruhi perkembangan ekonomi. Berbagai transaksi jual beli yang sebelumnya hanya bisa dilakukan dengan cara tatap muka (dan sebagian sangat kecil melalui pos atau telepon), kini sangat mudah dan sering dilakukan melalui Internet. Transaksi melalui Internet ini dikenal dengan nama e-commerce.
Terkait dengan pemerintahan, Internet juga memicu tumbuhnya transparansi pelaksanaan pemerintahan melalui e-government.
[sunting] Tata tertib Internet
Sama seperti halnya sebuah komunitas, Internet juga mempunyai tata tertib tertentu, yang dikenal dengan nama Nettiquette.
[sunting] Isu moral dan undang-undang
Terdapat kebimbangan masyarakat tentang Internet yang berpuncak pada beberapa bahan kontroversi di dalamnya. Pelanggaran hak cipta, pornografi, pencurian identitas, dan pernyataan kebencian (hate speech), adalah biasa dan sulit dijaga. Hingga tahun 2007, Indonesia masih belum memiliki Cyberlaw, padahal draft akademis RUU Cyberlaw sudah dibahas sejak tahun 2000 oleh Ditjen Postel dan Deperindag. UU yang masih ada kaitannya dengan teknologi informasi dan telekomunikasi adalah UU Telekomunikasi tahun 1999.
Internet juga disalahkan oleh sebagian orang karena dianggap menjadi sebab kematian. Brandon Vedas meninggal dunia akibat pemakaian narkotik yang melampaui batas dengan semangat dari teman-teman chatting IRCnya. Shawn Woolley bunuh diri karena ketagihan dengan permainan online, Everquest. Brandes ditikam bunuh, dan dimakan oleh Armin Meiwes setelah menjawab iklan dalam internet.
[sunting] Akses Internet
Negara dengan akses internet yang terbaik termasuk Korea Selatan (50% daripada penduduknya mempunyai akses jalurlebar - Broadband), dan Swedia. Terdapat dua bentuk akses internet yang umum, yaitu dial-up, dan jalurlebar. Di Indonesia, seperti negara berkembang dimana akses Internet dan penetrasi PC masih juga rendah, lainnya sekitar 42% dari akses Internet melalui fasilitas Public Internet akses seperti warnet , cybercafe, hotspot dll. Tempat umum lainnya yang sering dipakai untuk akses internet adalah di kampus dan di kantor.
Disamping menggunakan PC (Personal Computer), kita juga bisa mengakses Internet melalui Handphone (HP) menggunakan Fasilitas yang disebut GPRS (General Packet Radio Service). GPRS merupakan salah satu standar komunikasi wireless (nirkabel) yang memiliki kecepatan koneksi 115 kbps dan mendukung aplikasi yang lebih luas (grafis dan multimedia). Teknologi GPRS dapat diakses yang mendukung fasilitas tersebut. Pen-setting-an GPRS pada ponsel Tergantung dari operator (Telkomsel, Indosat, XL, 3) yang digunakan. Biaya akses Internet dihitung melalui besarnya kapasitas (per-kilobite) yang didownload.
[sunting] Penggunaan Internet di tempat umum
Internet juga semakin banyak digunakan di tempat umum. Beberapa tempat umum yang menyediakan layanan internet termasuk perpustakaan, dan internet cafe/warnet (juga disebut Cyber Cafe). Terdapat juga tempat awam yang menyediakan pusat akses internet, seperti Internet Kiosk, Public access Terminal, dan Telepon web.
Terdapat juga toko-toko yang menyediakan akses wi-fi, seperti Wifi-cafe. Pengguna hanya perlu membawa laptop (notebook), atau PDA, yang mempunyai kemampuan wifi untuk mendapatkan akses internet.
ass ...
welcome to my world ...
Minggu, 08 November 2009
MICROSOFT
Microsoft Corporation (NASDAQ: MSFT, didirikan 1975), berkantor pusat di Redmond, Washington, Amerika Serikat, adalah perusahaan perangkat lunak terbesar di dunia (dengan lebih dari 50.000 karyawan di berbagai negara, hingga Mei 2004).
Microsoft mengembangkan, membuat, melisensikan dan mendukung beragam jenis produk software untuk berbagai peralatan perkomputeran. Produknya yang paling terkenal adalah kelompok sistem operasi Microsoft Windows, yang telah ada di mana-mana dalam pasar komputer desktop.
Strategi bisnis Microsoft yang agresif telah mengakibatkan beberapa penyelidikan pemerintah, termasuk tuntutan hukum federal pada tahun 1998 di mana Microsoft dinyatakan telah secara ilegal menggunakan kekuatan monopolinya untuk mengalahkan pesaingnya; melalui aksi banding dan negosiasi, Microsoft telah mengurangi pengaruh dari keputusan ini pada pengoperasian perusahaan dan status keuangannya.
[sunting] Produk dan organisasi
Microsoft menjual beragam produk software. Banyak dari produk tersebut dikembangkan secara internal, misalnya Microsoft Basic. Beberapa produk dibeli dari pihak lainnya lalu dimerek ulang oleh Microsoft untuk distribusinya, seperti Microsoft Project, sebuah program manajemen proyek; Visio, sebuah program pentabelan; DoubleSpace; Virtual PC yang dibeli dari Connectix; dan bahkan MS-DOS sendiri, yang menjadi awal kesuksesan Microsoft dalam dunia pembuatan dan pemasaran perangkat lunak.
Microsoft mengembangkan, membuat, melisensikan dan mendukung beragam jenis produk software untuk berbagai peralatan perkomputeran. Produknya yang paling terkenal adalah kelompok sistem operasi Microsoft Windows, yang telah ada di mana-mana dalam pasar komputer desktop.
Strategi bisnis Microsoft yang agresif telah mengakibatkan beberapa penyelidikan pemerintah, termasuk tuntutan hukum federal pada tahun 1998 di mana Microsoft dinyatakan telah secara ilegal menggunakan kekuatan monopolinya untuk mengalahkan pesaingnya; melalui aksi banding dan negosiasi, Microsoft telah mengurangi pengaruh dari keputusan ini pada pengoperasian perusahaan dan status keuangannya.
[sunting] Produk dan organisasi
Microsoft menjual beragam produk software. Banyak dari produk tersebut dikembangkan secara internal, misalnya Microsoft Basic. Beberapa produk dibeli dari pihak lainnya lalu dimerek ulang oleh Microsoft untuk distribusinya, seperti Microsoft Project, sebuah program manajemen proyek; Visio, sebuah program pentabelan; DoubleSpace; Virtual PC yang dibeli dari Connectix; dan bahkan MS-DOS sendiri, yang menjadi awal kesuksesan Microsoft dalam dunia pembuatan dan pemasaran perangkat lunak.
Microsoft Infopath
Microsoft InfoPath (nama lengkapnya adalah Microsoft Office InfoPath) adalah sebuah program aplikasi yang digunakan untuk mengembangkan formulir pemasukan data berbasis XML, yang dirilis pertama kali sebagai bagian dari Microsoft Office System 2003, dan kini menjadi bagian dari Microsoft Office System 2007. Ketika dikembangkan, InfoPath memiliki nama kode XDocs, dan menawarkan fitur-fitur seperti kemampuannya untuk membuat dan menampilkan dokumen XML dengan dukungan terhadap skema XML yang didefinisikan sendiri. Aplikasi ini juga dapat dikonfigurasikan agar dapat terhubung terhadap sistem eksternal dengan menggunakan XML Web Services melalui Microsoft XML Parser (MSXML) dan SOAP Toolkit. Selain itu, sistem back-end dan middle-tier juga dapat dikonfigurasikan agar dapat berkomunikasi dengannya dengan menggunakan standar-standar layanan Web seperti SOAP, UDDI, dan WSDL. Mengingat InfoPath adalah program pengolah XML, maka adalah mungkin mengolah data tersebut dengan menggunakan pengolah XML lainnya.
Microsoft Power Point
Microsoft PowerPoint adalah sebuah program komputer untuk presentasi yang dikembangkan oleh Microsoft di dalam paket aplikasi kantoran mereka, Microsoft Office, selain Microsoft Word, Excel, Access dan beberapa program lainnya. PowerPoint berjalan di atas komputer PC berbasis sistem operasi Microsoft Windows dan juga Apple Macintosh yang menggunakan sistem operasi Apple Mac OS, meskipun pada awalnya aplikasi ini berjalan di atas sistem operasi Xenix. Aplikasi ini sangat banyak digunakan, apalagi oleh kalangan perkantoran dan pebisnis, para pendidik, siswa, dan trainer. Dimulai pada versi Microsoft Office System 2003, Microsoft mengganti nama dari sebelumnya Microsoft PowerPoint saja menjadi Microsoft Office PowerPoint. Versi terbaru dari PowerPoint adalah versi 12 (Microsoft Office PowerPoint 2007), yang tergabung ke dalam paket Microsoft Office System 2007.
Daftar isi [sembunyikan]
1 Sejarah
2 Versi
3 Operasi
4 Kompatibilitas
[sunting] Sejarah
Aplikasi Microsoft PowerPoint ini pertama kali dikembangkan oleh Bob Gaskins dan Dennis Austin sebagai Presenter untuk perusahaan bernama Forethought, Inc yang kemudian mereka ubah namanya menjadi PowerPoint.
Pada tahun 1987, PowerPoint versi 1.0 dirilis, dan komputer yang didukungnya adalah Apple Macintosh. PowerPoint kala itu masih menggunakan warna hitam/putih, yang mampu membuat halaman teks dan grafik untuk transparansi overhead projector (OHP). Setahun kemudian, versi baru dari PowerPoint muncul dengan dukungan warna, setelah Macintosh berwarna muncul ke pasaran.
Microsoft pun mengakuisisi Forethought, Inc dan tentu saja perangkat lunak PowerPoint dengan harga kira-kira 14 Juta dolar pada tanggal 31 Juli 1987. Pada tahun 1990, versi Microsoft Windows dari PowerPoint (versi 2.0) muncul ke pasaran, mengikuti jejak Microsoft Windows 3.0. Sejak tahun 1990, PowerPoint telah menjadi bagian standar yang tidak terpisahkan dalam paket aplikasi kantoran Microsoft Office System (kecuali Basic Edition).
Versi terbaru adalah Microsoft Office PowerPoint 2007 (PowerPoint 12), yang dirilis pada bulan November 2006, yang merupakan sebuah lompatan yang cukup jauh dari segi antarmuka pengguna dan kemampuan grafik yang ditingkatkan. Selain itu, dibandingkan dengan format data sebelumnya yang merupakan data biner dengan ekstensi *.ppt, versi ini menawarkan format data XML dengan ekstensi *.pptx.
Operasi
Dalam PowerPoint, seperti halnya perangkat lunak pengolah presentasi lainnya, objek teks, grafik, video, suara, dan objek-objek lainnya diposisikan dalam beberapa halaman individual yang disebut dengan "slide". Istilah slide dalam PowerPoint ini memiliki analogi yang sama dengan slide dalam proyektor biasa, yang telah kuno, akibat munculnya perangkat lunak komputer yang mampu mengolah presentasi semacam PowerPoint dan Impress. Setiap slide dapat dicetak atau ditampilkan dalam layar dan dapat dinavigasikan melalui perintah dari si presenter. Slide juga dapat membentuk dasar webcast (sebuah siaran di World Wide Web).
PowerPoint menawarkan dua jenis properti pergerakan, yakni Custom Animations dan Transition. Properti pergerakan Entrance, Emphasis, dan Exit objek dalam sebuah slide dapat diatur oleh Custom Animation, sementara Transition mengatur pergerakan dari satu slide ke slide lainnya. Semuanya dapat dianimaskan dalam banyak cara. Desain keseluruhan dari sebuah presentasi dapat diatur dengan menggunakaan Master Slide, dan struktur keseluruhan dari prsentasi dapat disunting dengan menggunakan Primitive Outliner (Outline).
PowerPoint dapat menyimpan presentasi dalam beberapa format, yakni sebagai berikut:
*.PPT (PowerPoint Presentation), yang merupakan data biner dan tersedia dalam semua versi PowerPoint (termasuk PowerPoint 12)
*.PPS (PowerPoint Show), yang merupakan data biner dan tersedia dalam semua versi PowerPoint (termasuk PowerPoint 12)
*.POT (PowerPoint Template), yang merupakan data biner dan tersedia dalam semua versi PowerPoint (termasuk PowerPoint 12)
*.PPTX (PowerPoint Presentation), yang yang merupakan data dalam bentuk XML dan hanya tersedia dalam PowerPoint 12.
[sunting] Kompatibilitas
Mengingat Microsoft PowerPoint merupakan program yang sangat populer, banyak aplikasi yang juga mendukung struktur data dari Microsoft PowerPoint, seperti halnya OpenOffice.org. OpenOffice.org Impress|Impress dan Apple Keynote. Hal ini menjadikan program-program tersebut dapat juga digunakan sebagai alternatif untuk PowerPoint, karena selain tentunya dapat membuka format PowerPoint, aplikasi-aplikasi tersebut tentunya memiliki fitur-fitur yang tidak dimiliki oleh PowerPoint.
Meskipun demikian, karena PowerPoint memiliki fitur untuk memasukkan konten dari aplikasi lainnya yang mendukung Object Linking and Embedding (OLE), beberapa presentasi sangat bergantung pada platform Windows, berarti aplikasi lainnya, bahkan PowerPoint untuk Macintosh sekalipun akan susah untuk membuka presentasi tersebut, dan bahkan kadang-kadang tidak dapat membukanya secara sukses dalam Macintosh. Hal ini mengakibatkan adanya kecenderungan para pengguna untuk menggunakan format dengan struktur data yang terbuka, seperti halnya Portable Document Format (PDF) dan juga OpenDocument dari OASIS yang digunakan oleh OpenOffice.org dan tentunya meninggalkan PowerPoint. Microsoft juga sebenarnya sudah melakukan hal serupa saat merilis format presentasi berbasis XML (PowerPoint 12), meskipun hingga saat ini masih banyak pengguna yang tetap menggunakan PowerPoint 11 (Microsoft Office PowerPoint 2003) yang masih berbasis data biner.
Daftar isi [sembunyikan]
1 Sejarah
2 Versi
3 Operasi
4 Kompatibilitas
[sunting] Sejarah
Aplikasi Microsoft PowerPoint ini pertama kali dikembangkan oleh Bob Gaskins dan Dennis Austin sebagai Presenter untuk perusahaan bernama Forethought, Inc yang kemudian mereka ubah namanya menjadi PowerPoint.
Pada tahun 1987, PowerPoint versi 1.0 dirilis, dan komputer yang didukungnya adalah Apple Macintosh. PowerPoint kala itu masih menggunakan warna hitam/putih, yang mampu membuat halaman teks dan grafik untuk transparansi overhead projector (OHP). Setahun kemudian, versi baru dari PowerPoint muncul dengan dukungan warna, setelah Macintosh berwarna muncul ke pasaran.
Microsoft pun mengakuisisi Forethought, Inc dan tentu saja perangkat lunak PowerPoint dengan harga kira-kira 14 Juta dolar pada tanggal 31 Juli 1987. Pada tahun 1990, versi Microsoft Windows dari PowerPoint (versi 2.0) muncul ke pasaran, mengikuti jejak Microsoft Windows 3.0. Sejak tahun 1990, PowerPoint telah menjadi bagian standar yang tidak terpisahkan dalam paket aplikasi kantoran Microsoft Office System (kecuali Basic Edition).
Versi terbaru adalah Microsoft Office PowerPoint 2007 (PowerPoint 12), yang dirilis pada bulan November 2006, yang merupakan sebuah lompatan yang cukup jauh dari segi antarmuka pengguna dan kemampuan grafik yang ditingkatkan. Selain itu, dibandingkan dengan format data sebelumnya yang merupakan data biner dengan ekstensi *.ppt, versi ini menawarkan format data XML dengan ekstensi *.pptx.
Operasi
Dalam PowerPoint, seperti halnya perangkat lunak pengolah presentasi lainnya, objek teks, grafik, video, suara, dan objek-objek lainnya diposisikan dalam beberapa halaman individual yang disebut dengan "slide". Istilah slide dalam PowerPoint ini memiliki analogi yang sama dengan slide dalam proyektor biasa, yang telah kuno, akibat munculnya perangkat lunak komputer yang mampu mengolah presentasi semacam PowerPoint dan Impress. Setiap slide dapat dicetak atau ditampilkan dalam layar dan dapat dinavigasikan melalui perintah dari si presenter. Slide juga dapat membentuk dasar webcast (sebuah siaran di World Wide Web).
PowerPoint menawarkan dua jenis properti pergerakan, yakni Custom Animations dan Transition. Properti pergerakan Entrance, Emphasis, dan Exit objek dalam sebuah slide dapat diatur oleh Custom Animation, sementara Transition mengatur pergerakan dari satu slide ke slide lainnya. Semuanya dapat dianimaskan dalam banyak cara. Desain keseluruhan dari sebuah presentasi dapat diatur dengan menggunakaan Master Slide, dan struktur keseluruhan dari prsentasi dapat disunting dengan menggunakan Primitive Outliner (Outline).
PowerPoint dapat menyimpan presentasi dalam beberapa format, yakni sebagai berikut:
*.PPT (PowerPoint Presentation), yang merupakan data biner dan tersedia dalam semua versi PowerPoint (termasuk PowerPoint 12)
*.PPS (PowerPoint Show), yang merupakan data biner dan tersedia dalam semua versi PowerPoint (termasuk PowerPoint 12)
*.POT (PowerPoint Template), yang merupakan data biner dan tersedia dalam semua versi PowerPoint (termasuk PowerPoint 12)
*.PPTX (PowerPoint Presentation), yang yang merupakan data dalam bentuk XML dan hanya tersedia dalam PowerPoint 12.
[sunting] Kompatibilitas
Mengingat Microsoft PowerPoint merupakan program yang sangat populer, banyak aplikasi yang juga mendukung struktur data dari Microsoft PowerPoint, seperti halnya OpenOffice.org. OpenOffice.org Impress|Impress dan Apple Keynote. Hal ini menjadikan program-program tersebut dapat juga digunakan sebagai alternatif untuk PowerPoint, karena selain tentunya dapat membuka format PowerPoint, aplikasi-aplikasi tersebut tentunya memiliki fitur-fitur yang tidak dimiliki oleh PowerPoint.
Meskipun demikian, karena PowerPoint memiliki fitur untuk memasukkan konten dari aplikasi lainnya yang mendukung Object Linking and Embedding (OLE), beberapa presentasi sangat bergantung pada platform Windows, berarti aplikasi lainnya, bahkan PowerPoint untuk Macintosh sekalipun akan susah untuk membuka presentasi tersebut, dan bahkan kadang-kadang tidak dapat membukanya secara sukses dalam Macintosh. Hal ini mengakibatkan adanya kecenderungan para pengguna untuk menggunakan format dengan struktur data yang terbuka, seperti halnya Portable Document Format (PDF) dan juga OpenDocument dari OASIS yang digunakan oleh OpenOffice.org dan tentunya meninggalkan PowerPoint. Microsoft juga sebenarnya sudah melakukan hal serupa saat merilis format presentasi berbasis XML (PowerPoint 12), meskipun hingga saat ini masih banyak pengguna yang tetap menggunakan PowerPoint 11 (Microsoft Office PowerPoint 2003) yang masih berbasis data biner.
Komputer
Komputer adalah alat yang dipakai untuk mengolah data menurut prosedur yang telah dirumuskan. Kata computer semula dipergunakan untuk menggambarkan orang yang perkerjaannya melakukan perhitungan aritmatika, dengan atau tanpa alat bantu, tetapi arti kata ini kemudian dipindahkan kepada mesin itu sendiri. Asal mulanya, pengolahan informasi hampir eksklusif berhubungan dengan masalah aritmatika, tetapi komputer modern dipakai untuk banyak tugas yang tidak berhubungan dengan matematika.
Dalam definisi seperti itu terdapat alat seperti slide rule, jenis kalkulator mekanik mulai dari abakus dan seterusnya, sampai semua komputer elektronik yang kontemporer. Istilah lebih baik yang cocok untuk arti luas seperti "komputer" adalah "yang memproses informasi" atau "sistem pengolah informasi."
Menurut sejarah komputer, generasi komputer dibagi menjadi 5 bagian.
Daftar isi
[sembunyikan]
* 1 Etimologi
* 2 Komputer
o 2.1 Komputer benam
o 2.2 Komputer pribadi
* 3 Bagaimana komputer bekerja
o 3.1 Memori
o 3.2 Pemrosesan
o 3.3 Input dan hasil
o 3.4 Instruksi
o 3.5 Arsitektur
o 3.6 Program
+ 3.6.1 Sistem operasi
* 4 Penggunaan komputer
* 5 Bagian-bagian komputer
o 5.1 Perangkat keras
o 5.2 Perangkat lunak
o 5.3 Slot pada komputer
* 6 Jenis komputer
* 7 Lihat pula
* 8 Pranala luar
[sunting] Etimologi
Selama bertahun-tahun sudah ada beberapa arti yang berbeda pada kata "komputer", dan beberapa kata berbeda tersebut sekarang cukup disebut disebut sebagai komputer.
Kata computer secara umum pernah dipergunakan untuk mendefiniskan orang yang melakukan perhitungan aritmatika, dengan atau tanpa mesin pembantu. Menurut Barnhart Concise Dictionary of Etymology, kata tersebut digunakan dalam bahasa Inggris pada tahun 1646 sebagai kata untuk "orang yang menghitung" kemudian menjelang 1897 juga digunakan sebagai "alat hitung mekanis". Selama Perang Dunia II kata tersebut menunjuk kepada para pekerja wanita Amerika Serikat dan Inggris yang pekerjaannya menghitung jalan artileri perang dengan mesin hitung.
Charles Babbage mendesain salah satu mesin hitung pertama yang disebut mesin analitikal. Selain itu, berbagai alat mesin sederhana seperti slide rule juga sudah dapat dikatakan sebagai komputer.
[sunting] Komputer
Rapikan
Bagian artikel ini perlu dirapikan. Bantulah kami untuk melakukannya.
Sekalipun demikian, definisi di atas mencakup banyak alat khusus yang hanya bisa memperhitungkan satu atau beberapa fungsi. Ketika mempertimbangkan komputer modern, sifat mereka yang paling penting yang membedakan mereka dari alat menghitung yang lebih awal ialah bahwa, dengan pemrograman yang benar, semua komputer dapat mengemulasi sifat apa pun (meskipun barangkali dibatasi oleh kapasitas penyimpanan dan kecepatan yang berbeda), dan, memang dipercaya bahwa mesin sekarang bisa meniru alat perkomputeran yang akan kita ciptakan di masa depan (meskipun niscaya lebih lambat). Dalam suatu pengertian, batas kemampuan ini adalah tes yang berguna karena mengenali komputer "maksud umum" dari alat maksud istimewa yang lebih awal. Definisi dari "maksud umum" bisa diformulasikan ke dalam syarat bahwa suatu mesin harus dapat meniru Mesin Turing universal. Mesin yang mendapat definisi ini dikenal sebagai Turing-lengkap, dan yang pertama mereka muncul pada tahun 1940 di tengah kesibukan perkembangan di seluruh dunia. Lihat artikel sejarah perkomputeran untuk lebih banyak detail periode ini.
[sunting] Komputer benam
Pada sekitar 20 tahun , banyak alat rumah tangga, khususnya termasuk panel dari permainan video tetapi juga mencakup telepon genggam, perekam kaset video, PDA dan banyak sekali dalam rumahtangga, industri, otomotif, dan alat elektronik lain, semua berisi sirkuit elektronik yang seperti komputer yang memenuhi syarat Turing-lengkap di atas (dengan catatan bahwa program dari alat ini seringkali dibuat secara langsung di dalam chip ROM yang akan perlu diganti untuk mengubah program mesin). Komputer maksud khusus lainnya secara umum dikenal sebagai "mikrokontroler" atau "komputer benam" (embedded computer). Oleh karena itu, banyak yang membatasi definisi komputer kepada alat yang maksud pokoknya adalah pengolahan informasi, daripada menjadi bagian dari sistem yang lebih besar seperti telepon, oven mikrowave, atau pesawat terbang, dan bisa diubah untuk berbagai maksud oleh pemakai tanpa modifikasi fisik. Komputer kerangka utama, minikomputer, dan komputer pribadi (PC) adalah macam utama komputer yang mendapat definisi ini.
[sunting] Komputer pribadi
Akhirnya, banyak orang yang tak akrab dengan bentuk komputer lain memakai istilah ini secara eksklusif untuk menunjuk kepada komputer pribadi (PC).
[sunting] Bagaimana komputer bekerja
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Saat teknologi yang dipakai pada komputer digital sudah berganti secara dramatis sejak komputer pertama pada tahun 1940-an (lihat Sejarah perangkat keras menghitung untuk lebih banyak detail), komputer kebanyakan masih menggunakan arsitektur Von Neumann, yang diusulkan di awal 1940-an oleh John von Neumann.
Arsitektur Von Neumann menggambarkan komputer dengan empat bagian utama: Unit Aritmatika dan Logis (ALU), unit kontrol, memori, dan alat masukan dan hasil (secara kolektif dinamakan I/O). Bagian ini dihubungkan oleh berkas kawat, "bus"
[sunting] Memori
modul memori RAM
Di sistem ini, memori adalah urutan byte yang dinomori (seperti "sel" atau "lubang burung dara"), masing-masing berisi sepotong kecil informasi. Informasi ini mungkin menjadi perintah untuk mengatakan pada komputer apa yang harus dilakukan. Sel mungkin berisi data yang diperlukan komputer untuk melakukan suatu perintah. Setiap slot mungkin berisi salah satu, dan apa yang sekarang menjadi data mungkin saja kemudian menjadi perintah.
Memori menyimpan berbagai bentuk informasi sebagai angka biner. Informasi yang belum berbentuk biner akan dipecahkan (encoded) dengan sejumlah instruksi yang mengubahnya menjadi sebuah angka atau urutan angka-angka. Sebagai contoh: Huruf F disimpan sebagai angka desimal 70 (atau angka biner ) menggunakan salah satu metode pemecahan. Instruksi yang lebih kompleks bisa digunakan untuk menyimpan gambar, suara, video, dan berbagai macam informasi. Informasi yang bisa disimpan dalam satu sell dinamakan sebuah byte.
Secara umum, memori bisa ditulis kembali lebih jutaan kali - memori dapat diumpamakan sebagai papan tulis dan kapur yang dapat ditulis dan dihapus kembali, daripada buku tulis dengan pena yang tidak dapat dihapus.
Ukuran masing-masing sel, dan jumlah sel, berubah secara hebat dari komputer ke komputer, dan teknologi dalam pembuatan memori sudah berubah secara hebat - dari relay elektromekanik, ke tabung yang diisi dengan air raksa (dan kemudian pegas) di mana pulsa akustik terbentuk, sampai matriks magnet permanen, ke setiap transistor, ke sirkuit terpadu dengan jutaan transistor di atas satu chip silikon.
[sunting] Pemrosesan
Unit Pemproses Pusat atau CPU ( central processing unit) berperanan untuk memproses arahan, melaksanakan pengiraan dan menguruskan laluan informasi menerusi system komputer. Unit atau peranti pemprosesan juga akan berkomunikasi dengan peranti input , output dan storan bagi melaksanakan arahan-arahan berkaitan.
Berkas:CPU with pins.jpg
Contoh sebuah CPU dalam kemasan Ball Grid Array (BGA) ditampilkan terbalik dengan menunjukan kaki-kakinya
Dalam arsitektur von Neumann yang asli, ia menjelaskan sebuah Unit Aritmatika dan Logika, dan sebuah Unit Kontrol. Dalam komputer-komputer modern, kedua unit ini terletak dalam satu sirkuit terpadu (IC - Integrated Circuit), yang biasanya disebut CPU (Central Processing Unit).
Unit Aritmatika dan Logika, atau Arithmetic Logic Unit (ALU), adalah alat yang melakukan pelaksanaan dasar seperti pelaksanaan aritmatika (tambahan, pengurangan, dan semacamnya), pelaksanaan logis (AND, OR, NOT), dan pelaksanaan perbandingan (misalnya, membandingkan isi sebanyak dua slot untuk kesetaraan). Pada unit inilah dilakukan "kerja" yang nyata.
Unit kontrol menyimpan perintah sekarang yang dilakukan oleh komputer, memerintahkan ALU untuk melaksanaan dan mendapat kembali informasi (dari memori) yang diperlukan untuk melaksanakan perintah itu, dan memindahkan kembali hasil ke lokasi memori yang sesuai. Sekali yang terjadi, unit kontrol pergi ke perintah berikutnya (biasanya ditempatkan di slot berikutnya, kecuali kalau perintah itu adalah perintah lompatan yang memberitahukan kepada komputer bahwa perintah berikutnya ditempatkan di lokasi lain).
[sunting] Input dan hasil
I/O membolehkan komputer mendapatkan informasi dari dunia luar, dan menaruh hasil kerjanya di sana, dapat berbentuk fisik (hardcopy) atau non fisik (softcopy). Ada berbagai macam alat I/O, dari yang akrab keyboard, monitor dan disk drive, ke yang lebih tidak biasa seperti webcam (kamera web, printer, scanner, dan sebagainya.
Yang dimiliki oleh semua alat masukan biasa ialah bahwa mereka meng-encode (mengubah) informasi dari suatu macam ke dalam data yang bisa diolah lebih lanjut oleh sistem komputer digital. Alat output, men-decode data ke dalam informasi yang bisa dimengerti oleh pemakai komputer. Dalam pengertian ini, sistem komputer digital adalah contoh sistem pengolah data.
[sunting] Instruksi
Perintah yang dibicarakan di atas bukan perintah seperti bahasa manusiawi. Komputer hanya mempunyai dalam jumlah terbatas perintah sederhana yang dirumuskan dengan baik. Perintah biasa yang dipahami kebanyakan komputer ialah "menyalin isi sel 123, dan tempat tiruan di sel 456", "menambahkan isi sel 666 ke sel 042, dan tempat akibat di sel 013", dan "jika isi sel 999 adalah 0, perintah berikutnya anda di sel 345".
Instruksi diwakili dalam komputer sebagai nomor - kode untuk "menyalin" mungkin menjadi 001, misalnya. Suatu himpunan perintah khusus yang didukung oleh komputer tertentu diketahui sebagai bahasa mesin komputer. Dalam prakteknya, orang biasanya tidak menulis perintah untuk komputer secara langsung di bahasa mesin tetapi memakai bahasa pemrograman "tingkat tinggi" yang kemudian diterjemahkan ke dalam bahasa mesin secara otomatis oleh program komputer khusus (interpreter dan kompiler). Beberapa bahasa pemrograman berhubungan erat dengan bahasa mesin, seperti assembler (bahasa tingkat rendah); di sisi lain, bahasa seperti Prolog didasarkan pada prinsip abstrak yang jauh dari detail pelaksanaan sebenarnya oleh mesin (bahasa tingkat tinggi)
[sunting] Arsitektur
Komputer kontemporer menaruh ALU dan unit kontrol ke dalam satu sirkuit terpadu yang dikenal sebagai Central Processing Unit atau CPU. Biasanya, memori komputer ditempatkan di atas beberapa sirkuit terpadu yang kecil dekat CPU. Alat yang menempati sebagian besar ruangan dalam komputer adalah ancilliary sistem (misalnya, untuk menyediakan tenaga listrik) atau alat I/O.
Beberapa komputer yang lebih besar berbeda dari model di atas di satu hal utama - mereka mempunyai beberapa CPU dan unit kontrol yang bekerja secara bersamaan. Terlebih lagi, beberapa komputer, yang dipakai sebagian besar untuk maksud penelitian dan perkomputeran ilmiah, sudah berbeda secara signifikan dari model di atas, tetapi mereka sudah menemukan sedikit penggunaan komersial.
Fungsi dari komputer secara prinsip sebenarnya cukup sederhana. Komputer mencapai perintah dan data dari memorinya. Perintah dilakukan, hasil disimpan, dan perintah berikutnya dicapai. Prosedur ini berulang sampai komputer dimatikan.
[sunting] Program
Program komputer adalah daftar besar perintah untuk dilakukan oleh komputer, barangkali dengan data di dalam tabel. Banyak program komputer berisi jutaan perintah, dan banyak dari perintah itu dilakukan berulang kali. Suatu [[Personal computer[PC]] modern yang umum (pada tahun 2003) bisa melakukan sekitar 2-3 milyar perintah dalam sedetik. Komputer tidak mendapat kemampuan luar biasa mereka lewat kemampuan untuk melakukan perintah kompleks. Tetapi, mereka melakukan jutaan perintah sederhana yang diatur oleh orang pandai, "programmer." "Programmer Baik memperkembangkan set-set perintah untuk melakukan tugas biasa (misalnya, menggambar titik di layar) dan lalu membuat set-set perintah itu tersedia kepada programmer lain." Dewasa ini, kebanyakan komputer kelihatannya melakukan beberapa program sekaligus. Ini biasanya diserahkan ke sebagai multitasking. Pada kenyataannya, CPU melakukan perintah dari satu program, kemudian setelah beberapa saat, CPU beralih ke program kedua dan melakukan beberapa perintahnya. Jarak waktu yang kecil ini sering diserahkan ke sebagai irisan waktu (time-slice). Ini menimbulkan khayal program lipat ganda yang dilakukan secara bersamaan dengan memberikan waktu CPU di antara program. Ini mirip bagaimana film adalah rangkaian kilat saja masih membingkaikan. Sistem operasi adalah program yang biasanya menguasai kali ini membagikan
[sunting] Sistem operasi
Sistem operasi ialah semacam gabungan dari potongan kode yang berguna. Ketika semacam kode komputer dapat dipakai secara bersama oleh beraneka-macam program komputer, setelah bertahun-tahun, programer akhirnya menmindahkannya ke dalam sistem operasi.
Sistem operasi, menentukan program yang mana dijalankan, kapan, dan alat yang mana (seperti memori atau I/O) yang mereka gunakan. Sistem operasi juga memberikan servis kepada program lain, seperti kode (driver) yang membolehkan programer untuk menulis program untuk suatu mesin tanpa perlu mengetahui detail dari semua alat elektronik yang terhubung.
[sunting] Penggunaan komputer
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Anak-anak sedang menggunakan komputer
Komputer digital pertama, dengan ukuran dan biaya yang besar, sebagian besar mengerjakan perhitungan ilmiah. ENIAC, komputer awal AS semula didesain untuk memperhitungkan tabel ilmu balistik untuk persenjataan (artileri), menghitung kerapatan penampang neutron untuk melihat jika bom hidrogen akan bekerja dengan semestinya (perhitungan ini, yang dilakukan pada Desember 1945 sampai Januari 1946 dan melibatkan dala dalam lebih dari satu juta kartu punch, memperlihatkan bentuk lalu di bawah pertimbangan akan gagal). CSIR Mk I, komputer pertama Australia, mengevaluasi pola curah hujan untuk tempat penampungan dari Snowy Mountains, suatu proyek pembangkitan hidroelektrik besar. Yang lainnya juga dipakai dalam kriptanalisis, misalnya komputer elektronik digital yang pertama, Colossus, dibuat selama Perang Dunia II. Akan tetapi, visionaris awal juga menyangka bahwa pemrograman itu akan membolehkan main catur, memindahkan gambar dan penggunaan lain.
Orang-orang di pemerintah dan perusahaan besar juga memakai komputer untuk mengotomasikan banyak koleksi data dan mengerjakan tugas yang sebelumnya dikerjakan oleh manusia - misalnya, memelihara dan memperbarui rekening dan inventaris. Dalam bidang pendidikan, ilmuwan di berbagai bidang mulai memakai komputer untuk analisa mereka sendiri. Penurunan harga komputer membuat mereka dapat dipakai oleh organisasi yang lebih kecil. Bisnis, organisasi, dan pemerintah sering menggunakan amat banyak komputer kecil untuk menyelesaikan tugas bahwa dulunya dilakukan oleh komputer kerangka utama yang mahal dan besar. Kumpulan komputer yang lebih kecil di satu lokasi diserahkan ke sebagai perkebunan server.
Dengan penemuan mikroprosesor di 1970-an, menjadi mungkin menghasilkan komputer yang sangat murah. PC menjadi populer untuk banyak tugas, termasuk menyimpan buku, menulis dan mencetak dokumen. Perhitungan meramalkan dan lain berulang matematika dengan spreadsheet, berhubungan dengan e-pos dan, Internet. Namun, ketersediaan luas komputer dan mudah customization sudah melihat mereka dipakai untuk banyak maksud lain.
Sekaligus, komputer kecil, biasanya dengan mengatur memprogram, mulai menemukan cara mereka ke dalam alat lain seperti peralatan rumah, mobil, pesawat terbang, dan perlengkapan industri. Yang ini prosesor benam menguasai kelakuan alat seperti itu yang lebih mudah, membolehkan kelakuan kontrol yang lebih kompleks (untuk kejadian, perkembangan anti-kunci rem di mobil). Saat abad kedua puluh satu dimulai, kebanyakan alat listrik, kebanyakan bentuk angkutan bertenaga, dan kebanyakan batas produksi pabrik dikuasai di samping komputer. Kebanyakan insinyur meramalkan bahwa ini cenderung kepada akan terus.
[sunting] Bagian-bagian komputer
Komputer terdiri atas 2 bagian besar yaitu perangkat lunak (software) dan perangkat keras (hardware).
[sunting] Perangkat keras
* Prosesor atau CPU sebagai unit yang mengolah data
* Memori RAM, tempat menyimpan data sementara
* Hard drive, media penyimpanan semi permanen
* Perangkat masukan, media yang digunakan untuk memasukkan data untuk diproses oleh CPU, seperti mouse, keyboard, dan tablet
* Perangkat keluaran, media yang digunakan untuk menampilkan hasil keluaran pemrosesan CPU, seperti monitor dan printer
[sunting] Perangkat lunak
* Sistem operasi
Program dasar pada komputer yang menghubungkan pengguna dengan hardware komputer. Sistem operasi yang biasa digunakan adalah Linux, Windows, dan Mac OS. Tugas sistem operasi termasuk (namun tidak hanya) mengatur eksekusi program di atasnya, koordinasi input, output, pemrosesan, memori, serta instalasi software.
* Program komputer
Merupakan aplikasi tambahan yang dipasang sesuai dengan sistem operasinya
[sunting] Slot pada komputer
* ISA/PCI, slot untuk masukan kartu tambahan non-grafis
* AGP/PCIe, slot untuk masukan kartu tambahan grafis
* IDE/SCSI/SATA, slot untuk hard drive/ODD
* USB, slot untuk masukan media plug-and-play (colok dan mainkan, artinya perangkat yang dapat dihubungkan ke komputer dan langsung dapat digunakan)
[sunting] Jenis komputer
* Komputer analog
* Komputer pulsa
* Mikrokomputer
o Komputer rumah (home computer)
o Komputer pribadi (PC)
o Server
* Minikomputer
* Mainframe computer
* Superkomputer
[sunting] Lihat pula
* Pameran komputer
* Ilmu komputer
* Komputasi
* Digital
* Sejarah komputer
* Perangkat keras komputer
* Perangkat lunak bebas
* KSpread
* Sound card
* KWord
* Weblog
* Laptop
* Desktop
* Tablet PC
Dalam definisi seperti itu terdapat alat seperti slide rule, jenis kalkulator mekanik mulai dari abakus dan seterusnya, sampai semua komputer elektronik yang kontemporer. Istilah lebih baik yang cocok untuk arti luas seperti "komputer" adalah "yang memproses informasi" atau "sistem pengolah informasi."
Menurut sejarah komputer, generasi komputer dibagi menjadi 5 bagian.
Daftar isi
[sembunyikan]
* 1 Etimologi
* 2 Komputer
o 2.1 Komputer benam
o 2.2 Komputer pribadi
* 3 Bagaimana komputer bekerja
o 3.1 Memori
o 3.2 Pemrosesan
o 3.3 Input dan hasil
o 3.4 Instruksi
o 3.5 Arsitektur
o 3.6 Program
+ 3.6.1 Sistem operasi
* 4 Penggunaan komputer
* 5 Bagian-bagian komputer
o 5.1 Perangkat keras
o 5.2 Perangkat lunak
o 5.3 Slot pada komputer
* 6 Jenis komputer
* 7 Lihat pula
* 8 Pranala luar
[sunting] Etimologi
Selama bertahun-tahun sudah ada beberapa arti yang berbeda pada kata "komputer", dan beberapa kata berbeda tersebut sekarang cukup disebut disebut sebagai komputer.
Kata computer secara umum pernah dipergunakan untuk mendefiniskan orang yang melakukan perhitungan aritmatika, dengan atau tanpa mesin pembantu. Menurut Barnhart Concise Dictionary of Etymology, kata tersebut digunakan dalam bahasa Inggris pada tahun 1646 sebagai kata untuk "orang yang menghitung" kemudian menjelang 1897 juga digunakan sebagai "alat hitung mekanis". Selama Perang Dunia II kata tersebut menunjuk kepada para pekerja wanita Amerika Serikat dan Inggris yang pekerjaannya menghitung jalan artileri perang dengan mesin hitung.
Charles Babbage mendesain salah satu mesin hitung pertama yang disebut mesin analitikal. Selain itu, berbagai alat mesin sederhana seperti slide rule juga sudah dapat dikatakan sebagai komputer.
[sunting] Komputer
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Sekalipun demikian, definisi di atas mencakup banyak alat khusus yang hanya bisa memperhitungkan satu atau beberapa fungsi. Ketika mempertimbangkan komputer modern, sifat mereka yang paling penting yang membedakan mereka dari alat menghitung yang lebih awal ialah bahwa, dengan pemrograman yang benar, semua komputer dapat mengemulasi sifat apa pun (meskipun barangkali dibatasi oleh kapasitas penyimpanan dan kecepatan yang berbeda), dan, memang dipercaya bahwa mesin sekarang bisa meniru alat perkomputeran yang akan kita ciptakan di masa depan (meskipun niscaya lebih lambat). Dalam suatu pengertian, batas kemampuan ini adalah tes yang berguna karena mengenali komputer "maksud umum" dari alat maksud istimewa yang lebih awal. Definisi dari "maksud umum" bisa diformulasikan ke dalam syarat bahwa suatu mesin harus dapat meniru Mesin Turing universal. Mesin yang mendapat definisi ini dikenal sebagai Turing-lengkap, dan yang pertama mereka muncul pada tahun 1940 di tengah kesibukan perkembangan di seluruh dunia. Lihat artikel sejarah perkomputeran untuk lebih banyak detail periode ini.
[sunting] Komputer benam
Pada sekitar 20 tahun , banyak alat rumah tangga, khususnya termasuk panel dari permainan video tetapi juga mencakup telepon genggam, perekam kaset video, PDA dan banyak sekali dalam rumahtangga, industri, otomotif, dan alat elektronik lain, semua berisi sirkuit elektronik yang seperti komputer yang memenuhi syarat Turing-lengkap di atas (dengan catatan bahwa program dari alat ini seringkali dibuat secara langsung di dalam chip ROM yang akan perlu diganti untuk mengubah program mesin). Komputer maksud khusus lainnya secara umum dikenal sebagai "mikrokontroler" atau "komputer benam" (embedded computer). Oleh karena itu, banyak yang membatasi definisi komputer kepada alat yang maksud pokoknya adalah pengolahan informasi, daripada menjadi bagian dari sistem yang lebih besar seperti telepon, oven mikrowave, atau pesawat terbang, dan bisa diubah untuk berbagai maksud oleh pemakai tanpa modifikasi fisik. Komputer kerangka utama, minikomputer, dan komputer pribadi (PC) adalah macam utama komputer yang mendapat definisi ini.
[sunting] Komputer pribadi
Akhirnya, banyak orang yang tak akrab dengan bentuk komputer lain memakai istilah ini secara eksklusif untuk menunjuk kepada komputer pribadi (PC).
[sunting] Bagaimana komputer bekerja
Rapikan
Bagian artikel ini perlu dirapikan. Bantulah kami untuk melakukannya.
Saat teknologi yang dipakai pada komputer digital sudah berganti secara dramatis sejak komputer pertama pada tahun 1940-an (lihat Sejarah perangkat keras menghitung untuk lebih banyak detail), komputer kebanyakan masih menggunakan arsitektur Von Neumann, yang diusulkan di awal 1940-an oleh John von Neumann.
Arsitektur Von Neumann menggambarkan komputer dengan empat bagian utama: Unit Aritmatika dan Logis (ALU), unit kontrol, memori, dan alat masukan dan hasil (secara kolektif dinamakan I/O). Bagian ini dihubungkan oleh berkas kawat, "bus"
[sunting] Memori
modul memori RAM
Di sistem ini, memori adalah urutan byte yang dinomori (seperti "sel" atau "lubang burung dara"), masing-masing berisi sepotong kecil informasi. Informasi ini mungkin menjadi perintah untuk mengatakan pada komputer apa yang harus dilakukan. Sel mungkin berisi data yang diperlukan komputer untuk melakukan suatu perintah. Setiap slot mungkin berisi salah satu, dan apa yang sekarang menjadi data mungkin saja kemudian menjadi perintah.
Memori menyimpan berbagai bentuk informasi sebagai angka biner. Informasi yang belum berbentuk biner akan dipecahkan (encoded) dengan sejumlah instruksi yang mengubahnya menjadi sebuah angka atau urutan angka-angka. Sebagai contoh: Huruf F disimpan sebagai angka desimal 70 (atau angka biner ) menggunakan salah satu metode pemecahan. Instruksi yang lebih kompleks bisa digunakan untuk menyimpan gambar, suara, video, dan berbagai macam informasi. Informasi yang bisa disimpan dalam satu sell dinamakan sebuah byte.
Secara umum, memori bisa ditulis kembali lebih jutaan kali - memori dapat diumpamakan sebagai papan tulis dan kapur yang dapat ditulis dan dihapus kembali, daripada buku tulis dengan pena yang tidak dapat dihapus.
Ukuran masing-masing sel, dan jumlah sel, berubah secara hebat dari komputer ke komputer, dan teknologi dalam pembuatan memori sudah berubah secara hebat - dari relay elektromekanik, ke tabung yang diisi dengan air raksa (dan kemudian pegas) di mana pulsa akustik terbentuk, sampai matriks magnet permanen, ke setiap transistor, ke sirkuit terpadu dengan jutaan transistor di atas satu chip silikon.
[sunting] Pemrosesan
Unit Pemproses Pusat atau CPU ( central processing unit) berperanan untuk memproses arahan, melaksanakan pengiraan dan menguruskan laluan informasi menerusi system komputer. Unit atau peranti pemprosesan juga akan berkomunikasi dengan peranti input , output dan storan bagi melaksanakan arahan-arahan berkaitan.
Berkas:CPU with pins.jpg
Contoh sebuah CPU dalam kemasan Ball Grid Array (BGA) ditampilkan terbalik dengan menunjukan kaki-kakinya
Dalam arsitektur von Neumann yang asli, ia menjelaskan sebuah Unit Aritmatika dan Logika, dan sebuah Unit Kontrol. Dalam komputer-komputer modern, kedua unit ini terletak dalam satu sirkuit terpadu (IC - Integrated Circuit), yang biasanya disebut CPU (Central Processing Unit).
Unit Aritmatika dan Logika, atau Arithmetic Logic Unit (ALU), adalah alat yang melakukan pelaksanaan dasar seperti pelaksanaan aritmatika (tambahan, pengurangan, dan semacamnya), pelaksanaan logis (AND, OR, NOT), dan pelaksanaan perbandingan (misalnya, membandingkan isi sebanyak dua slot untuk kesetaraan). Pada unit inilah dilakukan "kerja" yang nyata.
Unit kontrol menyimpan perintah sekarang yang dilakukan oleh komputer, memerintahkan ALU untuk melaksanaan dan mendapat kembali informasi (dari memori) yang diperlukan untuk melaksanakan perintah itu, dan memindahkan kembali hasil ke lokasi memori yang sesuai. Sekali yang terjadi, unit kontrol pergi ke perintah berikutnya (biasanya ditempatkan di slot berikutnya, kecuali kalau perintah itu adalah perintah lompatan yang memberitahukan kepada komputer bahwa perintah berikutnya ditempatkan di lokasi lain).
[sunting] Input dan hasil
I/O membolehkan komputer mendapatkan informasi dari dunia luar, dan menaruh hasil kerjanya di sana, dapat berbentuk fisik (hardcopy) atau non fisik (softcopy). Ada berbagai macam alat I/O, dari yang akrab keyboard, monitor dan disk drive, ke yang lebih tidak biasa seperti webcam (kamera web, printer, scanner, dan sebagainya.
Yang dimiliki oleh semua alat masukan biasa ialah bahwa mereka meng-encode (mengubah) informasi dari suatu macam ke dalam data yang bisa diolah lebih lanjut oleh sistem komputer digital. Alat output, men-decode data ke dalam informasi yang bisa dimengerti oleh pemakai komputer. Dalam pengertian ini, sistem komputer digital adalah contoh sistem pengolah data.
[sunting] Instruksi
Perintah yang dibicarakan di atas bukan perintah seperti bahasa manusiawi. Komputer hanya mempunyai dalam jumlah terbatas perintah sederhana yang dirumuskan dengan baik. Perintah biasa yang dipahami kebanyakan komputer ialah "menyalin isi sel 123, dan tempat tiruan di sel 456", "menambahkan isi sel 666 ke sel 042, dan tempat akibat di sel 013", dan "jika isi sel 999 adalah 0, perintah berikutnya anda di sel 345".
Instruksi diwakili dalam komputer sebagai nomor - kode untuk "menyalin" mungkin menjadi 001, misalnya. Suatu himpunan perintah khusus yang didukung oleh komputer tertentu diketahui sebagai bahasa mesin komputer. Dalam prakteknya, orang biasanya tidak menulis perintah untuk komputer secara langsung di bahasa mesin tetapi memakai bahasa pemrograman "tingkat tinggi" yang kemudian diterjemahkan ke dalam bahasa mesin secara otomatis oleh program komputer khusus (interpreter dan kompiler). Beberapa bahasa pemrograman berhubungan erat dengan bahasa mesin, seperti assembler (bahasa tingkat rendah); di sisi lain, bahasa seperti Prolog didasarkan pada prinsip abstrak yang jauh dari detail pelaksanaan sebenarnya oleh mesin (bahasa tingkat tinggi)
[sunting] Arsitektur
Komputer kontemporer menaruh ALU dan unit kontrol ke dalam satu sirkuit terpadu yang dikenal sebagai Central Processing Unit atau CPU. Biasanya, memori komputer ditempatkan di atas beberapa sirkuit terpadu yang kecil dekat CPU. Alat yang menempati sebagian besar ruangan dalam komputer adalah ancilliary sistem (misalnya, untuk menyediakan tenaga listrik) atau alat I/O.
Beberapa komputer yang lebih besar berbeda dari model di atas di satu hal utama - mereka mempunyai beberapa CPU dan unit kontrol yang bekerja secara bersamaan. Terlebih lagi, beberapa komputer, yang dipakai sebagian besar untuk maksud penelitian dan perkomputeran ilmiah, sudah berbeda secara signifikan dari model di atas, tetapi mereka sudah menemukan sedikit penggunaan komersial.
Fungsi dari komputer secara prinsip sebenarnya cukup sederhana. Komputer mencapai perintah dan data dari memorinya. Perintah dilakukan, hasil disimpan, dan perintah berikutnya dicapai. Prosedur ini berulang sampai komputer dimatikan.
[sunting] Program
Program komputer adalah daftar besar perintah untuk dilakukan oleh komputer, barangkali dengan data di dalam tabel. Banyak program komputer berisi jutaan perintah, dan banyak dari perintah itu dilakukan berulang kali. Suatu [[Personal computer[PC]] modern yang umum (pada tahun 2003) bisa melakukan sekitar 2-3 milyar perintah dalam sedetik. Komputer tidak mendapat kemampuan luar biasa mereka lewat kemampuan untuk melakukan perintah kompleks. Tetapi, mereka melakukan jutaan perintah sederhana yang diatur oleh orang pandai, "programmer." "Programmer Baik memperkembangkan set-set perintah untuk melakukan tugas biasa (misalnya, menggambar titik di layar) dan lalu membuat set-set perintah itu tersedia kepada programmer lain." Dewasa ini, kebanyakan komputer kelihatannya melakukan beberapa program sekaligus. Ini biasanya diserahkan ke sebagai multitasking. Pada kenyataannya, CPU melakukan perintah dari satu program, kemudian setelah beberapa saat, CPU beralih ke program kedua dan melakukan beberapa perintahnya. Jarak waktu yang kecil ini sering diserahkan ke sebagai irisan waktu (time-slice). Ini menimbulkan khayal program lipat ganda yang dilakukan secara bersamaan dengan memberikan waktu CPU di antara program. Ini mirip bagaimana film adalah rangkaian kilat saja masih membingkaikan. Sistem operasi adalah program yang biasanya menguasai kali ini membagikan
[sunting] Sistem operasi
Sistem operasi ialah semacam gabungan dari potongan kode yang berguna. Ketika semacam kode komputer dapat dipakai secara bersama oleh beraneka-macam program komputer, setelah bertahun-tahun, programer akhirnya menmindahkannya ke dalam sistem operasi.
Sistem operasi, menentukan program yang mana dijalankan, kapan, dan alat yang mana (seperti memori atau I/O) yang mereka gunakan. Sistem operasi juga memberikan servis kepada program lain, seperti kode (driver) yang membolehkan programer untuk menulis program untuk suatu mesin tanpa perlu mengetahui detail dari semua alat elektronik yang terhubung.
[sunting] Penggunaan komputer
Rapikan
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Anak-anak sedang menggunakan komputer
Komputer digital pertama, dengan ukuran dan biaya yang besar, sebagian besar mengerjakan perhitungan ilmiah. ENIAC, komputer awal AS semula didesain untuk memperhitungkan tabel ilmu balistik untuk persenjataan (artileri), menghitung kerapatan penampang neutron untuk melihat jika bom hidrogen akan bekerja dengan semestinya (perhitungan ini, yang dilakukan pada Desember 1945 sampai Januari 1946 dan melibatkan dala dalam lebih dari satu juta kartu punch, memperlihatkan bentuk lalu di bawah pertimbangan akan gagal). CSIR Mk I, komputer pertama Australia, mengevaluasi pola curah hujan untuk tempat penampungan dari Snowy Mountains, suatu proyek pembangkitan hidroelektrik besar. Yang lainnya juga dipakai dalam kriptanalisis, misalnya komputer elektronik digital yang pertama, Colossus, dibuat selama Perang Dunia II. Akan tetapi, visionaris awal juga menyangka bahwa pemrograman itu akan membolehkan main catur, memindahkan gambar dan penggunaan lain.
Orang-orang di pemerintah dan perusahaan besar juga memakai komputer untuk mengotomasikan banyak koleksi data dan mengerjakan tugas yang sebelumnya dikerjakan oleh manusia - misalnya, memelihara dan memperbarui rekening dan inventaris. Dalam bidang pendidikan, ilmuwan di berbagai bidang mulai memakai komputer untuk analisa mereka sendiri. Penurunan harga komputer membuat mereka dapat dipakai oleh organisasi yang lebih kecil. Bisnis, organisasi, dan pemerintah sering menggunakan amat banyak komputer kecil untuk menyelesaikan tugas bahwa dulunya dilakukan oleh komputer kerangka utama yang mahal dan besar. Kumpulan komputer yang lebih kecil di satu lokasi diserahkan ke sebagai perkebunan server.
Dengan penemuan mikroprosesor di 1970-an, menjadi mungkin menghasilkan komputer yang sangat murah. PC menjadi populer untuk banyak tugas, termasuk menyimpan buku, menulis dan mencetak dokumen. Perhitungan meramalkan dan lain berulang matematika dengan spreadsheet, berhubungan dengan e-pos dan, Internet. Namun, ketersediaan luas komputer dan mudah customization sudah melihat mereka dipakai untuk banyak maksud lain.
Sekaligus, komputer kecil, biasanya dengan mengatur memprogram, mulai menemukan cara mereka ke dalam alat lain seperti peralatan rumah, mobil, pesawat terbang, dan perlengkapan industri. Yang ini prosesor benam menguasai kelakuan alat seperti itu yang lebih mudah, membolehkan kelakuan kontrol yang lebih kompleks (untuk kejadian, perkembangan anti-kunci rem di mobil). Saat abad kedua puluh satu dimulai, kebanyakan alat listrik, kebanyakan bentuk angkutan bertenaga, dan kebanyakan batas produksi pabrik dikuasai di samping komputer. Kebanyakan insinyur meramalkan bahwa ini cenderung kepada akan terus.
[sunting] Bagian-bagian komputer
Komputer terdiri atas 2 bagian besar yaitu perangkat lunak (software) dan perangkat keras (hardware).
[sunting] Perangkat keras
* Prosesor atau CPU sebagai unit yang mengolah data
* Memori RAM, tempat menyimpan data sementara
* Hard drive, media penyimpanan semi permanen
* Perangkat masukan, media yang digunakan untuk memasukkan data untuk diproses oleh CPU, seperti mouse, keyboard, dan tablet
* Perangkat keluaran, media yang digunakan untuk menampilkan hasil keluaran pemrosesan CPU, seperti monitor dan printer
[sunting] Perangkat lunak
* Sistem operasi
Program dasar pada komputer yang menghubungkan pengguna dengan hardware komputer. Sistem operasi yang biasa digunakan adalah Linux, Windows, dan Mac OS. Tugas sistem operasi termasuk (namun tidak hanya) mengatur eksekusi program di atasnya, koordinasi input, output, pemrosesan, memori, serta instalasi software.
* Program komputer
Merupakan aplikasi tambahan yang dipasang sesuai dengan sistem operasinya
[sunting] Slot pada komputer
* ISA/PCI, slot untuk masukan kartu tambahan non-grafis
* AGP/PCIe, slot untuk masukan kartu tambahan grafis
* IDE/SCSI/SATA, slot untuk hard drive/ODD
* USB, slot untuk masukan media plug-and-play (colok dan mainkan, artinya perangkat yang dapat dihubungkan ke komputer dan langsung dapat digunakan)
[sunting] Jenis komputer
* Komputer analog
* Komputer pulsa
* Mikrokomputer
o Komputer rumah (home computer)
o Komputer pribadi (PC)
o Server
* Minikomputer
* Mainframe computer
* Superkomputer
[sunting] Lihat pula
* Pameran komputer
* Ilmu komputer
* Komputasi
* Digital
* Sejarah komputer
* Perangkat keras komputer
* Perangkat lunak bebas
* KSpread
* Sound card
* KWord
* Weblog
* Laptop
* Desktop
* Tablet PC
Scanner
In computing, a scanner is a device that optically scans images, printed text, handwriting, or an object, and converts it to a digital image. Common examples found in offices are variations of the desktop (or flatbed) scanner where the document is placed on a glass window for scanning. Hand-held scanners, where the device is moved by hand, have evolved from text scanning "wands" to 3D scanners used for industrial design, reverse engineering, test and measurement, orthotics, gaming and other applications. Mechanically driven scanners that move the document are typically used for large-format documents, where a flatbed design would be impractical.
Modern scanners typically use a charge-coupled device (CCD) or a Contact Image Sensor (CIS) as the image sensor, whereas older drum scanners use a photomultiplier tube as the image sensor. A rotary scanner, used for high-speed document scanning, is another type of drum scanner, using a CCD array instead of a photomultiplier. Other types of scanners are planetary scanners, which take photographs of books and documents, and 3D scanners, for producing three-dimensional models of objects.
Another category of scanner is digital camera scanners, which are based on the concept of reprographic cameras. Due to increasing resolution and new features such as anti-shake, digital cameras have become an attractive alternative to regular scanners. While still having disadvantages compared to traditional scanners (such as distortion, reflections, shadows, low contrast), digital cameras offer advantages such as speed, portability, gentle digitizing of thick documents without damaging the book spine. New scanning technologies are combining 3D scanners with digital cameras to create full-color, photo-realistic 3D models of objects.
In the biomedical research area, detection devices for DNA microarrays are called scanners as well. These scanners are high-resolution systems (up to 1 µm/ pixel), similar to microscopes. The detection is done via CCD or a photomultiplier tube (PMT).
Contents [hide]
1 Historical precedent
2 Types
2.1 Drum
2.2 Flatbed
2.3 Film
2.4 Hand
3 Quality
4 Computer connection
4.1 Direct physical connection to a computer
4.2 Indirect (network) connection to a computer
4.3 Applications Programming Interface
4.4 Bundled applications
5 Output data
6 Document processing
7 Infrared cleaning
8 Trivia
8.1 Scanner Music
8.2 Scanner art
9 See also
10 References
11 External links
[edit] Historical precedent
Édouard Belin and his BelinographScanners can be considered the successors of early telephotography input devices, consisting of a rotating drum with a single photodetector at a standard speed of 60 or 120 rpm (later models up to 240 rpm). They send a linear analog AM signal through standard telephone voice lines to receptors, which synchronously print the proportional intensity on special paper. This system was in use in press from the 1920s to the mid-1990s. Color photos were sent as three separated RGB filtered images consecutively, but only for special events due to transmission costs.
[edit] Types
[edit] Drum
Drum scanners capture image information with photomultiplier tubes (PMT), rather than the charge-coupled device (CCD) arrays found in flatbed scanners and inexpensive film scanners. Reflective and transmissive originals are mounted on an acrylic cylinder, the scanner drum, which rotates at high speed while it passes the object being scanned in front of precision optics that deliver image information to the PMTs. Most modern color drum scanners use 3 matched PMTs, which read red, blue, and green light respectively. Light from the original artwork is split into separate red, blue, and green beams in the optical bench of the scanner.
The drum scanner gets its name from the clear acrylic cylinder, the drum, on which the original artwork is mounted for scanning. Depending on size it is possible to mount originals up to 11"x17", but maximum size varies by manufacturer. One of the unique features of drum scanners is the ability to control sample area and aperture size independently. The sample size is the area that the scanner encoder reads to create an individual pixel. The aperture is the actual opening that allows light into the optical bench of the scanner. The ability to control aperture and sample size separately is particularly useful for smoothing film grain when scanning black-and white and color negative originals.
While drum scanners are capable of scanning both reflective and transmissive artwork, a good-quality flatbed scanner can produce good scans from reflective artwork. As a result, drum scanners are rarely used to scan prints now that high quality inexpensive flatbed scanners are readily available. Film, however, is where drum scanners continue to be the tool of choice for high-end applications. Because film can be wet-mounted to the scanner drum and because of the exceptional sensitivity of the PMTs, drum scanners are capable of capturing very subtle details in film originals.
Only a few companies continue to manufacture drum scanners. While prices of both new and used units have come down over the last decade, they still require a considerable monetary investment when compared to CCD flatbed and film scanners. However, drum scanners remain in demand due to their capacity to produce scans that are superior in resolution, color gradation, and value structure. Also, since drum scanners are capable of resolutions up to 12,000 PPI, their use is generally recommended when a scanned image is going to be enlarged.
The first scanned imageIn most graphic-arts operations, very-high-quality flatbed scanners have replaced drum scanners, being both less expensive and faster. However, drum scanners continue to be used in high-end applications, such as museum-quality archiving of photographs and print production of high-quality books and magazine advertisements. In addition, due to the greater availability of pre-owned units many fine-art photographers are acquiring drum scanners, which has created a new niche market for the machines.
The first image scanner ever developed was a drum scanner. It was built in 1957 at the US National Bureau of Standards by a team led by Russell Kirsch. The first image ever scanned on this machine was a 5 cm square photograph of Kirsch's then-three-month-old son, Walden. The black and white image had a resolution of 176 pixels on a side.[1]
[edit] Flatbed
A flatbed scanner is usually composed of a glass pane (or platen), under which there is a bright light (often xenon or cold cathode fluorescent) which illuminates the pane, and a moving optical array in CCD scanning. CCD type scanners typically contain three rows (arrays) of sensors with red, green, and blue filters. CIS scanning consists of a moving set of red, green and blue LEDs strobed for illumination and a connected monochromatic photodiode array for light collection. Images to be scanned are placed face down on the glass, an opaque cover is lowered over it to exclude ambient light, and the sensor array and light source move across the pane, reading the entire area. An image is therefore visible to the detector only because of the light it reflects. Transparent images do not work in this way, and require special accessories that illuminate them from the upper side. Many scanners offer this as an option.
[edit] Film
DSLR camera and slide scanner"Slide" (positive) or negative film can be scanned in equipment specially manufactured for this purpose. Usually, uncut film strips of up to six frames, or four mounted slides, are inserted in a carrier, which is moved by a stepper motor across a lens and CCD sensor inside the scanner. Some models mainly used for same-size scans.
[edit] Hand
Hand scanners come in two forms: document and 3D scanners. Hand held document scanners are manual devices that are dragged across the surface of the image to be scanned. Scanning documents in this manner requires a steady hand, as an uneven scanning rate would produce distorted images - a little light on the scanner would indicate if the motion was too fast. They typically have a "start" button, which is held by the user for the duration of the scan; some switches to set the optical resolution; and a roller, which generates a clock pulse for synchronization with the computer. Most hand scanners were monochrome, and produced light from an array of green LEDs to illuminate the image. A typical hand scanner also had a small window through which the document being scanned could be viewed. They were popular during the early 1990s and usually had a proprietary interface module specific to a particular type of computer, usually an Atari ST or Commodore Amiga.
While popularity for document scanning has waned, use of hand held 3D scanners remains popular for many applications, including industrial design, reverse engineering, inspection & analysis, digital manufacturing and medical applications. To compensate for the uneven motion of the human hand, most 3D scanning systems rely on the placement of reference markers – typically adhesive reflective tabs that the scanner uses to align elements and mark positions in space.
[edit] Quality
Scanners typically read red-green-blue color (RGB) data from the array. This data is then processed with some proprietary algorithm to correct for different exposure conditions, and sent to the computer via the device's input/output interface (usually SCSI or bidirectional parallel port in machines pre-dating the USB standard). Color depth varies depending on the scanning array characteristics, but is usually at least 24 bits. High quality models have 48 bits or more color depth. The other qualifying parameter for a scanner is its resolution, measured in pixels per inch (ppi), sometimes more accurately referred to as Samples per inch (spi). Instead of using the scanner's true optical resolution, the only meaningful parameter, manufacturers like to refer to the interpolated resolution, which is much higher thanks to software interpolation. As of 2009[update], a high-end flatbed scanner can scan up to 5400 ppi and a good drum scanner has an optical resolution of 12,000 ppi.
Manufacturers often claim interpolated resolutions as high as 19,200 ppi; but such numbers carry little meaningful value, because the number of possible interpolated pixels is unlimited.
The size of the file created increases with the square of the resolution; doubling the resolution quadruples the file size. A resolution must be chosen that is within the capabilities of the equipment, preserves sufficient detail, and does not produce a file of excessive size. The file size can be reduced for a given resolution by using "lossy" compression methods such as JPEG, at some cost in quality. If the best possible quality is required lossless compression should be used; reduced-quality files of smaller size can be produced from such an image when required (e.g., image designed to be printed on a full page, and a much smaller file to be displayed as part of a fast-loading web page).
The third important parameter for a scanner is its density range. A high density range means that the scanner is able to reproduce shadow details and brightness details in one scan.
By combining full-color imagery with 3D models, modern hand-held scanners are able to completely reproduce objects electronically. The addition of 3D color printers enables accurate miniaturization of these objects, with applications across many industries and professions.
[edit] Computer connection
Scanning the document is only one part of the process. For the scanned image to be useful, it must be transferred from the scanner to an application running on the computer. There are two basic issues: (1) how the scanner is physically connected to the computer and (2) how the application retrieves the information from the scanner.
[edit] Direct physical connection to a computer
The amount of data generated by a scanner can be very large: a 600 DPI 9"x11" (slightly larger than A4 paper) uncompressed 24-bit image is about 100 megabytes of data which must be transferred and stored. Recent scanners can generate this volume of data in a matter of seconds, making a fast connection desirable.
Scanners communicate to their host computer using one of the following physical interfaces, listing from slow to fast:
Parallel - Connecting through a parallel port is the slowest common transfer method. Early scanners had parallel port connections that could not transfer data faster than 70 kilobytes/second. The primary advantage of the parallel port connection was economic: it avoided adding an interface card to the computer.
GPIB - General Purpose Interface Bus. Certain drumscanners like the Howtek D4000 featured both a SCSI and GPIB interface. The latter conforms to the IEEE-488 standard, introduced in the mid ’70's. The GPIB-interface has only been used by a few scanner manufactures, mostly serving the DOS/Windows environment. For Apple Macintosh systems, National Instruments provided a NuBus GPIB interface card.
Small Computer System Interface (SCSI), which is supported by most computers only via an additional SCSI interface card. Some SCSI scanners are supplied together with a dedicated SCSI card for a PC, although any SCSI controller can be used. During the evolution of the SCSI standard speeds increased, with backwards compatibility; a SCSI connection can transfer data at the highest speed which both the controller and the device support. SCSI has been largely replaced by USB and Firewire, one or both of which are directly supported by most computers, and which are easier to set up than SCSI.
Universal Serial Bus (USB) scanners can transfer data quickly, and they are easier to use and cheaper than SCSI devices. The early USB 1.1 standard could transfer data at only 1.5 megabytes per second (slower than SCSI), but the later USB 2.0 standard can theoretically transfer up to 60 megabytes per second (although everyday rates are much lower), resulting in faster operation.
FireWire is an interface that is much faster than USB 1.1 and comparable to USB 2.0. FireWire speeds are 25, 50, and 100, 400 and 800 megabits per second (but a device may not support all speeds).
Some early scanners used a proprietary interface card rather than a standard interface.
[edit] Indirect (network) connection to a computer
During the early nineties, professional flatbed scanners were targeted to professional users. Some vendors (like Umax) allowed a single scanner connected to a host computer to function as a scanner accessible by all users within a local computer network. This proved to be very handy to e.g. publishers, print shops, etc. This functionality gradually disappeared after the mid-’90's as flatbed scanners became more affordable each year. However, as of 2000 and later, all-in-one multi-purpose devices targeted to serve both (small) offices and consumers usually combine a printer, scanner, copier and fax into a single apparatus available to a whole workgroup, providing each individual fax, scan, copy and print functionality.
[edit] Applications Programming Interface
An application such as Adobe Photoshop must communicate with the scanner. There are many different scanners, and many of those scanners use different protocols. In order to simplify applications programming, some Applications Programming Interfaces ("API") were developed. The API presents a uniform interface to the scanner. This means that the application does not need to know the specific details of the scanner in order to access it directly. For example, Adobe Photoshop supports the TWAIN standard; consequently, (in an ideal world) Photoshop can acquire an image from any scanner that also supports TWAIN.
In practice, there are often problems with an application communicating with a scanner. Either the application or the scanner manufacturer (or both) may have faults in their implementation of the API.
Typically, the API is implemented as a dynamically linked library. Each scanner manufacturer provides software that translates the API procedure calls into primitive commands that are issued to a hardware controller (such as the SCSI, USB, or FireWire controller). The manufacturer's part of the API is commonly called a device driver, but that designation is not strictly accurate: the API does not run in kernel mode and does not directly access the device.
Some scanner manufacturers will offer more than one API.
Most scanners use the TWAIN API. The TWAIN API, originally used for low-end and home-use equipment, is now widely used for large-volume scanning.
Other scanner API's are
ISIS, created by Pixel Translations, which still uses SCSI-II for performance reasons, is used by large, departmental-scale, machines.
SANE (Scanner Access Now Easy) is a free/open source API for accessing scanners. Originally developed for Unix and Linux operating systems, it has been ported to OS/2, Mac OS X, and Microsoft Windows. Unlike TWAIN, SANE does not handle the user interface. This allows batch scans and transparent network access without any special support from the device driver.
Windows Image Acquisition ("WIA") is an API provided by Microsoft.
[edit] Bundled applications
Although no software beyond a scanning utility is a feature of any scanner, many scanners come bundled with software. Typically, in addition to the scanning utility, some type of image-editing application (such as Photoshop), and optical character recognition (OCR) software are supplied. OCR software converts graphical images of text into standard text that can be edited using common word-processing and text-editing software; accuracy is rarely perfect.
[edit] Output data
The scanned result is a non-compressed RGB image, which can be transferred to a computer's memory. Some scanners compress and clean up the image using embedded firmware. Once on the computer, the image can be processed with a raster graphics program (such as Photoshop or the GIMP) and saved on a storage device (such as a hard disk).
Images are usually stored on a hard disk. Pictures are normally stored in image formats such as uncompressed Bitmap, "non-lossy" (lossless) compressed TIFF and PNG, and "lossy" compressed JPEG. Documents are best stored in TIFF or PDF format; JPEG is particularly unsuitable for text. Optical character recognition (OCR) software allows a scanned image of text to be converted into editable text with reasonable accuracy, so long as the text is cleanly printed and in a typeface and size that can be read by the software. OCR capability may be integrated into the scanning software, or the scanned image file can be processed with a separate OCR program.
[edit] Document processing
Document scannerThe scanning or digitization of paper documents for storage makes different requirements of the scanning equipment used than scanning of pictures for reproduction. While documents can be scanned on general-purpose scanners, it is more efficiently performed on dedicated document scanners manufactured by Atiz Innovation, Böwe Bell & Howell, Canon, Epson, Fujitsu, HP, Kodak and other companies.
When scanning large quantities of documents, speed and paper-handling is very important, but the resolution of the scan will normally be much lower than for good reproduction of pictures.
Document scanners have document feeders, usually larger than those sometimes found on copiers or all-purpose scanners. Scans are made at high speed, perhaps 20 to 150 pages per minute, often in grayscale, although many scanners support color. Many scanners can scan both sides of double-sided originals (duplex operation). Sophisticated document scanners have firmware or software that cleans up scans of text as they are produced, eliminating accidental marks and sharpening type; this would be unacceptable for photographic work, where marks cannot reliably be distinguished from desired fine detail. Files created are compressed as they are made.
The resolution used is usually from 150 to 300 dpi, although the hardware may be capable of somewhat higher resolution; this produces images of text good enough to read and for optical character recognition (OCR), without the higher demands on storage space required by higher-resolution images.
Document scans are often processed using OCR technology to create editable and searchable files. Most scanners use ISIS or TWAIN device drivers to scan documents into TIFF format so that the scanned pages can be fed into a document management system that will handle the archiving and retrieval of the scanned pages. Lossy JPEG compression, which is very efficient for pictures, is undesirable for text documents, as slanted straight edges take on a jagged appearance, and solid black (or other color) text on a light background compresses well with lossless compression formats.
While paper feeding and scanning can be done automatically and quickly, preparation and indexing are necessary and require much work by humans. Preparation involves manually inspecting the papers to be scanned and making sure that they are in order, unfolded, without staples or anything else that might jam the scanner. Additionally, some industries such as legal and medical may require documents to have Bates Numbering or some other mark giving a document identification number and date/time of the document scan.
Indexing involves associating keywords to files so that they can be retrieved by content. This process can sometimes be automated to some extent, but is likely to involve manual labour. One common practice is the use of barcode-recognition technology: during preparation, barcode sheets with folder names are inserted into the document files, folders, and document groups. Using automatic batch scanning, the documents are saved into the appropriate folders, and an index is created for integration into document-management software systems.
A specialized form of document scanning is book scanning. Technical difficulties arise from the books usually being bound and sometimes fragile and irreplaceable, but some manufacturers have developed specialized machinery to deal with this. For instance, Atiz DIY scanner uses a V-shaped cradle and a V-shaped transparent platen to handle brittle books. Often special robotic mechanisms are used to automate the page turning and scanning process.
[edit] Infrared cleaning
Main article: Infrared cleaning
Infrared cleaning is a technique used to remove dust and scratches from film, and most modern scanners incorporate this feature. It works by scanning the film with infrared light. From this, it is possible to detect dust and scratches that cut off the infrared light; and they can then be automatically removed, by considering their position, size, shape, and surroundings.
Scanner manufacturers usually have their own name attached to this technique. For example, Epson, Nikon, Microtek, and others use Digital ICE, while Canon uses its own system FARE (Film Automatic Retouching and Enhancement system).[2] Some independent software developers are designing their own infrared cleaning tools.
[edit] Trivia
[edit] Scanner Music
Flatbed scanners are capable of synthesising simple musical scores, due to the variable speed (and tone) of their stepper motors. This property can be applied for hardware diagnostics: for example the HP Scanjet 5 plays Ode to Joy if powered on with the Scan button held down and the SCSI ID set to zero.[3] Windows- and Linux-based software is available for several brands and types of flatbed scanners to play MIDI files for fun purposes.[4]
[edit] Scanner art
Main article: Scanography
Scanner art is art made by placing objects on a flatbed scanner and scanning them. There has been some debate as to whether scanner art is a form of digital photography.[citation needed] Images made with a scanner differ from those made with a camera, as the scanner has very little depth of field and a constant light all over the surface.
Modern scanners typically use a charge-coupled device (CCD) or a Contact Image Sensor (CIS) as the image sensor, whereas older drum scanners use a photomultiplier tube as the image sensor. A rotary scanner, used for high-speed document scanning, is another type of drum scanner, using a CCD array instead of a photomultiplier. Other types of scanners are planetary scanners, which take photographs of books and documents, and 3D scanners, for producing three-dimensional models of objects.
Another category of scanner is digital camera scanners, which are based on the concept of reprographic cameras. Due to increasing resolution and new features such as anti-shake, digital cameras have become an attractive alternative to regular scanners. While still having disadvantages compared to traditional scanners (such as distortion, reflections, shadows, low contrast), digital cameras offer advantages such as speed, portability, gentle digitizing of thick documents without damaging the book spine. New scanning technologies are combining 3D scanners with digital cameras to create full-color, photo-realistic 3D models of objects.
In the biomedical research area, detection devices for DNA microarrays are called scanners as well. These scanners are high-resolution systems (up to 1 µm/ pixel), similar to microscopes. The detection is done via CCD or a photomultiplier tube (PMT).
Contents [hide]
1 Historical precedent
2 Types
2.1 Drum
2.2 Flatbed
2.3 Film
2.4 Hand
3 Quality
4 Computer connection
4.1 Direct physical connection to a computer
4.2 Indirect (network) connection to a computer
4.3 Applications Programming Interface
4.4 Bundled applications
5 Output data
6 Document processing
7 Infrared cleaning
8 Trivia
8.1 Scanner Music
8.2 Scanner art
9 See also
10 References
11 External links
[edit] Historical precedent
Édouard Belin and his BelinographScanners can be considered the successors of early telephotography input devices, consisting of a rotating drum with a single photodetector at a standard speed of 60 or 120 rpm (later models up to 240 rpm). They send a linear analog AM signal through standard telephone voice lines to receptors, which synchronously print the proportional intensity on special paper. This system was in use in press from the 1920s to the mid-1990s. Color photos were sent as three separated RGB filtered images consecutively, but only for special events due to transmission costs.
[edit] Types
[edit] Drum
Drum scanners capture image information with photomultiplier tubes (PMT), rather than the charge-coupled device (CCD) arrays found in flatbed scanners and inexpensive film scanners. Reflective and transmissive originals are mounted on an acrylic cylinder, the scanner drum, which rotates at high speed while it passes the object being scanned in front of precision optics that deliver image information to the PMTs. Most modern color drum scanners use 3 matched PMTs, which read red, blue, and green light respectively. Light from the original artwork is split into separate red, blue, and green beams in the optical bench of the scanner.
The drum scanner gets its name from the clear acrylic cylinder, the drum, on which the original artwork is mounted for scanning. Depending on size it is possible to mount originals up to 11"x17", but maximum size varies by manufacturer. One of the unique features of drum scanners is the ability to control sample area and aperture size independently. The sample size is the area that the scanner encoder reads to create an individual pixel. The aperture is the actual opening that allows light into the optical bench of the scanner. The ability to control aperture and sample size separately is particularly useful for smoothing film grain when scanning black-and white and color negative originals.
While drum scanners are capable of scanning both reflective and transmissive artwork, a good-quality flatbed scanner can produce good scans from reflective artwork. As a result, drum scanners are rarely used to scan prints now that high quality inexpensive flatbed scanners are readily available. Film, however, is where drum scanners continue to be the tool of choice for high-end applications. Because film can be wet-mounted to the scanner drum and because of the exceptional sensitivity of the PMTs, drum scanners are capable of capturing very subtle details in film originals.
Only a few companies continue to manufacture drum scanners. While prices of both new and used units have come down over the last decade, they still require a considerable monetary investment when compared to CCD flatbed and film scanners. However, drum scanners remain in demand due to their capacity to produce scans that are superior in resolution, color gradation, and value structure. Also, since drum scanners are capable of resolutions up to 12,000 PPI, their use is generally recommended when a scanned image is going to be enlarged.
The first scanned imageIn most graphic-arts operations, very-high-quality flatbed scanners have replaced drum scanners, being both less expensive and faster. However, drum scanners continue to be used in high-end applications, such as museum-quality archiving of photographs and print production of high-quality books and magazine advertisements. In addition, due to the greater availability of pre-owned units many fine-art photographers are acquiring drum scanners, which has created a new niche market for the machines.
The first image scanner ever developed was a drum scanner. It was built in 1957 at the US National Bureau of Standards by a team led by Russell Kirsch. The first image ever scanned on this machine was a 5 cm square photograph of Kirsch's then-three-month-old son, Walden. The black and white image had a resolution of 176 pixels on a side.[1]
[edit] Flatbed
A flatbed scanner is usually composed of a glass pane (or platen), under which there is a bright light (often xenon or cold cathode fluorescent) which illuminates the pane, and a moving optical array in CCD scanning. CCD type scanners typically contain three rows (arrays) of sensors with red, green, and blue filters. CIS scanning consists of a moving set of red, green and blue LEDs strobed for illumination and a connected monochromatic photodiode array for light collection. Images to be scanned are placed face down on the glass, an opaque cover is lowered over it to exclude ambient light, and the sensor array and light source move across the pane, reading the entire area. An image is therefore visible to the detector only because of the light it reflects. Transparent images do not work in this way, and require special accessories that illuminate them from the upper side. Many scanners offer this as an option.
[edit] Film
DSLR camera and slide scanner"Slide" (positive) or negative film can be scanned in equipment specially manufactured for this purpose. Usually, uncut film strips of up to six frames, or four mounted slides, are inserted in a carrier, which is moved by a stepper motor across a lens and CCD sensor inside the scanner. Some models mainly used for same-size scans.
[edit] Hand
Hand scanners come in two forms: document and 3D scanners. Hand held document scanners are manual devices that are dragged across the surface of the image to be scanned. Scanning documents in this manner requires a steady hand, as an uneven scanning rate would produce distorted images - a little light on the scanner would indicate if the motion was too fast. They typically have a "start" button, which is held by the user for the duration of the scan; some switches to set the optical resolution; and a roller, which generates a clock pulse for synchronization with the computer. Most hand scanners were monochrome, and produced light from an array of green LEDs to illuminate the image. A typical hand scanner also had a small window through which the document being scanned could be viewed. They were popular during the early 1990s and usually had a proprietary interface module specific to a particular type of computer, usually an Atari ST or Commodore Amiga.
While popularity for document scanning has waned, use of hand held 3D scanners remains popular for many applications, including industrial design, reverse engineering, inspection & analysis, digital manufacturing and medical applications. To compensate for the uneven motion of the human hand, most 3D scanning systems rely on the placement of reference markers – typically adhesive reflective tabs that the scanner uses to align elements and mark positions in space.
[edit] Quality
Scanners typically read red-green-blue color (RGB) data from the array. This data is then processed with some proprietary algorithm to correct for different exposure conditions, and sent to the computer via the device's input/output interface (usually SCSI or bidirectional parallel port in machines pre-dating the USB standard). Color depth varies depending on the scanning array characteristics, but is usually at least 24 bits. High quality models have 48 bits or more color depth. The other qualifying parameter for a scanner is its resolution, measured in pixels per inch (ppi), sometimes more accurately referred to as Samples per inch (spi). Instead of using the scanner's true optical resolution, the only meaningful parameter, manufacturers like to refer to the interpolated resolution, which is much higher thanks to software interpolation. As of 2009[update], a high-end flatbed scanner can scan up to 5400 ppi and a good drum scanner has an optical resolution of 12,000 ppi.
Manufacturers often claim interpolated resolutions as high as 19,200 ppi; but such numbers carry little meaningful value, because the number of possible interpolated pixels is unlimited.
The size of the file created increases with the square of the resolution; doubling the resolution quadruples the file size. A resolution must be chosen that is within the capabilities of the equipment, preserves sufficient detail, and does not produce a file of excessive size. The file size can be reduced for a given resolution by using "lossy" compression methods such as JPEG, at some cost in quality. If the best possible quality is required lossless compression should be used; reduced-quality files of smaller size can be produced from such an image when required (e.g., image designed to be printed on a full page, and a much smaller file to be displayed as part of a fast-loading web page).
The third important parameter for a scanner is its density range. A high density range means that the scanner is able to reproduce shadow details and brightness details in one scan.
By combining full-color imagery with 3D models, modern hand-held scanners are able to completely reproduce objects electronically. The addition of 3D color printers enables accurate miniaturization of these objects, with applications across many industries and professions.
[edit] Computer connection
Scanning the document is only one part of the process. For the scanned image to be useful, it must be transferred from the scanner to an application running on the computer. There are two basic issues: (1) how the scanner is physically connected to the computer and (2) how the application retrieves the information from the scanner.
[edit] Direct physical connection to a computer
The amount of data generated by a scanner can be very large: a 600 DPI 9"x11" (slightly larger than A4 paper) uncompressed 24-bit image is about 100 megabytes of data which must be transferred and stored. Recent scanners can generate this volume of data in a matter of seconds, making a fast connection desirable.
Scanners communicate to their host computer using one of the following physical interfaces, listing from slow to fast:
Parallel - Connecting through a parallel port is the slowest common transfer method. Early scanners had parallel port connections that could not transfer data faster than 70 kilobytes/second. The primary advantage of the parallel port connection was economic: it avoided adding an interface card to the computer.
GPIB - General Purpose Interface Bus. Certain drumscanners like the Howtek D4000 featured both a SCSI and GPIB interface. The latter conforms to the IEEE-488 standard, introduced in the mid ’70's. The GPIB-interface has only been used by a few scanner manufactures, mostly serving the DOS/Windows environment. For Apple Macintosh systems, National Instruments provided a NuBus GPIB interface card.
Small Computer System Interface (SCSI), which is supported by most computers only via an additional SCSI interface card. Some SCSI scanners are supplied together with a dedicated SCSI card for a PC, although any SCSI controller can be used. During the evolution of the SCSI standard speeds increased, with backwards compatibility; a SCSI connection can transfer data at the highest speed which both the controller and the device support. SCSI has been largely replaced by USB and Firewire, one or both of which are directly supported by most computers, and which are easier to set up than SCSI.
Universal Serial Bus (USB) scanners can transfer data quickly, and they are easier to use and cheaper than SCSI devices. The early USB 1.1 standard could transfer data at only 1.5 megabytes per second (slower than SCSI), but the later USB 2.0 standard can theoretically transfer up to 60 megabytes per second (although everyday rates are much lower), resulting in faster operation.
FireWire is an interface that is much faster than USB 1.1 and comparable to USB 2.0. FireWire speeds are 25, 50, and 100, 400 and 800 megabits per second (but a device may not support all speeds).
Some early scanners used a proprietary interface card rather than a standard interface.
[edit] Indirect (network) connection to a computer
During the early nineties, professional flatbed scanners were targeted to professional users. Some vendors (like Umax) allowed a single scanner connected to a host computer to function as a scanner accessible by all users within a local computer network. This proved to be very handy to e.g. publishers, print shops, etc. This functionality gradually disappeared after the mid-’90's as flatbed scanners became more affordable each year. However, as of 2000 and later, all-in-one multi-purpose devices targeted to serve both (small) offices and consumers usually combine a printer, scanner, copier and fax into a single apparatus available to a whole workgroup, providing each individual fax, scan, copy and print functionality.
[edit] Applications Programming Interface
An application such as Adobe Photoshop must communicate with the scanner. There are many different scanners, and many of those scanners use different protocols. In order to simplify applications programming, some Applications Programming Interfaces ("API") were developed. The API presents a uniform interface to the scanner. This means that the application does not need to know the specific details of the scanner in order to access it directly. For example, Adobe Photoshop supports the TWAIN standard; consequently, (in an ideal world) Photoshop can acquire an image from any scanner that also supports TWAIN.
In practice, there are often problems with an application communicating with a scanner. Either the application or the scanner manufacturer (or both) may have faults in their implementation of the API.
Typically, the API is implemented as a dynamically linked library. Each scanner manufacturer provides software that translates the API procedure calls into primitive commands that are issued to a hardware controller (such as the SCSI, USB, or FireWire controller). The manufacturer's part of the API is commonly called a device driver, but that designation is not strictly accurate: the API does not run in kernel mode and does not directly access the device.
Some scanner manufacturers will offer more than one API.
Most scanners use the TWAIN API. The TWAIN API, originally used for low-end and home-use equipment, is now widely used for large-volume scanning.
Other scanner API's are
ISIS, created by Pixel Translations, which still uses SCSI-II for performance reasons, is used by large, departmental-scale, machines.
SANE (Scanner Access Now Easy) is a free/open source API for accessing scanners. Originally developed for Unix and Linux operating systems, it has been ported to OS/2, Mac OS X, and Microsoft Windows. Unlike TWAIN, SANE does not handle the user interface. This allows batch scans and transparent network access without any special support from the device driver.
Windows Image Acquisition ("WIA") is an API provided by Microsoft.
[edit] Bundled applications
Although no software beyond a scanning utility is a feature of any scanner, many scanners come bundled with software. Typically, in addition to the scanning utility, some type of image-editing application (such as Photoshop), and optical character recognition (OCR) software are supplied. OCR software converts graphical images of text into standard text that can be edited using common word-processing and text-editing software; accuracy is rarely perfect.
[edit] Output data
The scanned result is a non-compressed RGB image, which can be transferred to a computer's memory. Some scanners compress and clean up the image using embedded firmware. Once on the computer, the image can be processed with a raster graphics program (such as Photoshop or the GIMP) and saved on a storage device (such as a hard disk).
Images are usually stored on a hard disk. Pictures are normally stored in image formats such as uncompressed Bitmap, "non-lossy" (lossless) compressed TIFF and PNG, and "lossy" compressed JPEG. Documents are best stored in TIFF or PDF format; JPEG is particularly unsuitable for text. Optical character recognition (OCR) software allows a scanned image of text to be converted into editable text with reasonable accuracy, so long as the text is cleanly printed and in a typeface and size that can be read by the software. OCR capability may be integrated into the scanning software, or the scanned image file can be processed with a separate OCR program.
[edit] Document processing
Document scannerThe scanning or digitization of paper documents for storage makes different requirements of the scanning equipment used than scanning of pictures for reproduction. While documents can be scanned on general-purpose scanners, it is more efficiently performed on dedicated document scanners manufactured by Atiz Innovation, Böwe Bell & Howell, Canon, Epson, Fujitsu, HP, Kodak and other companies.
When scanning large quantities of documents, speed and paper-handling is very important, but the resolution of the scan will normally be much lower than for good reproduction of pictures.
Document scanners have document feeders, usually larger than those sometimes found on copiers or all-purpose scanners. Scans are made at high speed, perhaps 20 to 150 pages per minute, often in grayscale, although many scanners support color. Many scanners can scan both sides of double-sided originals (duplex operation). Sophisticated document scanners have firmware or software that cleans up scans of text as they are produced, eliminating accidental marks and sharpening type; this would be unacceptable for photographic work, where marks cannot reliably be distinguished from desired fine detail. Files created are compressed as they are made.
The resolution used is usually from 150 to 300 dpi, although the hardware may be capable of somewhat higher resolution; this produces images of text good enough to read and for optical character recognition (OCR), without the higher demands on storage space required by higher-resolution images.
Document scans are often processed using OCR technology to create editable and searchable files. Most scanners use ISIS or TWAIN device drivers to scan documents into TIFF format so that the scanned pages can be fed into a document management system that will handle the archiving and retrieval of the scanned pages. Lossy JPEG compression, which is very efficient for pictures, is undesirable for text documents, as slanted straight edges take on a jagged appearance, and solid black (or other color) text on a light background compresses well with lossless compression formats.
While paper feeding and scanning can be done automatically and quickly, preparation and indexing are necessary and require much work by humans. Preparation involves manually inspecting the papers to be scanned and making sure that they are in order, unfolded, without staples or anything else that might jam the scanner. Additionally, some industries such as legal and medical may require documents to have Bates Numbering or some other mark giving a document identification number and date/time of the document scan.
Indexing involves associating keywords to files so that they can be retrieved by content. This process can sometimes be automated to some extent, but is likely to involve manual labour. One common practice is the use of barcode-recognition technology: during preparation, barcode sheets with folder names are inserted into the document files, folders, and document groups. Using automatic batch scanning, the documents are saved into the appropriate folders, and an index is created for integration into document-management software systems.
A specialized form of document scanning is book scanning. Technical difficulties arise from the books usually being bound and sometimes fragile and irreplaceable, but some manufacturers have developed specialized machinery to deal with this. For instance, Atiz DIY scanner uses a V-shaped cradle and a V-shaped transparent platen to handle brittle books. Often special robotic mechanisms are used to automate the page turning and scanning process.
[edit] Infrared cleaning
Main article: Infrared cleaning
Infrared cleaning is a technique used to remove dust and scratches from film, and most modern scanners incorporate this feature. It works by scanning the film with infrared light. From this, it is possible to detect dust and scratches that cut off the infrared light; and they can then be automatically removed, by considering their position, size, shape, and surroundings.
Scanner manufacturers usually have their own name attached to this technique. For example, Epson, Nikon, Microtek, and others use Digital ICE, while Canon uses its own system FARE (Film Automatic Retouching and Enhancement system).[2] Some independent software developers are designing their own infrared cleaning tools.
[edit] Trivia
[edit] Scanner Music
Flatbed scanners are capable of synthesising simple musical scores, due to the variable speed (and tone) of their stepper motors. This property can be applied for hardware diagnostics: for example the HP Scanjet 5 plays Ode to Joy if powered on with the Scan button held down and the SCSI ID set to zero.[3] Windows- and Linux-based software is available for several brands and types of flatbed scanners to play MIDI files for fun purposes.[4]
[edit] Scanner art
Main article: Scanography
Scanner art is art made by placing objects on a flatbed scanner and scanning them. There has been some debate as to whether scanner art is a form of digital photography.[citation needed] Images made with a scanner differ from those made with a camera, as the scanner has very little depth of field and a constant light all over the surface.
Printer
Printer (computing)
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A Lexmark printer
In computing, a printer is a peripheral which produces a hard copy (permanent readable text and/or graphics) of documents stored in electronic form, usually on physical print media such as paper or transparencies. Many printers are primarily used as local peripherals, and are attached by a printer cable or, in most newer printers, a USB cable to a computer which serves as a document source. Some printers, commonly known as network printers, have built-in network interfaces (typically wireless and/or Ethernet), and can serve as a hardcopy device for any user on the network. Individual printers are often designed to support both local and network connected users at the same time. In addition, a few modern printers can directly interface to electronic media such as memory sticks or memory cards, or to image capture devices such as digital cameras, scanners; some printers are combined with a scanners and/or fax machines in a single unit, and can function as photocopiers. Printers that include non-printing features are sometimes called Multifunction printers (MFP), Multi-Function Devices (MFD), or All-In-One (AIO) printers. Most MFPs include printing, scanning, and copying among their features.
A Virtual printer is a piece of computer software whose user interface and API resemble that of a printer driver, but which is not connected with a physical computer printer.
Printers are designed for low-volume, short-turnaround print jobs; requiring virtually no setup time to achieve a hard copy of a given document. However, printers are generally slow devices (30 pages per minute is considered fast; and many inexpensive consumer printers are far slower than that), and the cost per page is actually relatively high. However this is offset by the on-demand convenience and project management costs being more controllable compared to an out-sourced solution. The printing press naturally remains the machine of choice for high-volume, professional publishing. However, as printers have improved in quality and performance, many jobs which used to be done by professional print shops are now done by users on local printers; see desktop publishing. The world's first computer printer was a 19th century mechanically driven apparatus invented by Charles Babbage for his Difference Engine.[1]
Contents
[hide]
• 1 Printing technology
• 2 Modern print technology
o 2.1 Toner-based printers
o 2.2 Liquid inkjet printers
o 2.3 Solid ink printers
o 2.4 Dye-sublimation printers
o 2.5 Inkless printers
2.5.1 Thermal printers
2.5.2 UV printers
• 3 Obsolete and special-purpose printing technologies
o 3.1 Typewriter-derived printers
o 3.2 Teletypewriter-derived printers
o 3.3 Daisy wheel printers
o 3.4 Dot-matrix printers
o 3.5 Line printers
o 3.6 Pen-based plotters
• 4 Sales
• 5 Other printers
• 6 Printing mode
• 7 Monochrome, color and photo printers
• 8 The printer manufacturing business
• 9 Printing speed
• 10 See also
• 11 References
[edit] Printing technology
Printers are routinely classified by the underlying print technology they employ; numerous such technologies have been developed over the years. The choice of print engine has a substantial effect on what jobs a printer is suitable for, as different technologies are capable of different levels of image/text quality, print speed, low cost, noise; in addition, some technologies are inappropriate for certain types of physical media (such as carbon paper or transparencies).
Another aspect of printer technology that is often forgotten is resistance to alteration: liquid ink such as from an inkjet head or fabric ribbon becomes absorbed by the paper fibers, so documents printed with a liquid ink sublimation printer are more difficult to alter than documents printed with toner or solid inks, which do not penetrate below the paper surface.
Checks should either be printed with liquid ink or on special "check paper with toner anchorage".[1] For similar reasons carbon film ribbons for IBM Selectric typewriters bore labels warning against using them to type negotiable instruments such as checks. The machine-readable lower portion of a check, however, must be printed using MICR toner or ink. Banks and other clearing houses employ automation equipment that relies on the magnetic flux from these specially printed characters to function properly.
[edit] Modern print technology
The following printing technologies are routinely found in modern printers:
[edit] Toner-based printers
Main article: Laser printer
Toner-based printers work using the Xerographic principle that is used in most photocopiers: by adhering toner to a light-sensitive print drum, then using static electricity to transfer the toner to the printing medium to which it is fused with heat and pressure.
The most common type of toner-based printer is the laser printer, which uses precision lasers to cause toner adherence. Laser printers are known for high quality prints, good print speed, and a low (Black and White) cost-per-copy. They are the most common printer for many general-purpose office applications, but are much less common as consumer printers due to their high initial cost — although this cost is dropping.
Laser printers are available in both color and monochrome varieties.
Another toner based printer is the LED printer which uses an array of LEDs instead of a laser to cause toner adhesion to the print drum.
Recent research has also indicated that Laser printers emit potentially dangerous ultrafine particles, possibly causing health problems associated with respiration [1] and cause pollution equivalent to cigarettes.[2] The degree of particle emissions varies with age, model and design of each printer but is generally proportional to the amount of toner required. Furthermore, a well ventilated workspace would allow such ultrafine particles to disperse thus reducing the health side effects.
[edit] Liquid inkjet printers
Inkjet printers operate by propelling variably-sized droplets of liquid or molten material (ink) onto almost any sized page. They are the most common type of computer printer for the general consumer.
[edit] Solid ink printers
Main article: Solid ink
Solid Ink printers, also known as phase-change printers, are a type of thermal transfer printer. They use solid sticks of CMYK colored ink (similar in consistency to candle wax), which are melted and fed into a piezo crystal operated print-head. The printhead sprays the ink on a rotating, oil coated drum. The paper then passes over the print drum, at which time the image is transferred, or transfixed, to the page.
Solid ink printers are most commonly used as color office printers, and are excellent at printing on transparencies and other non-porous media. Solid ink printers can produce excellent results. Acquisition and operating costs are similar to laser printers. Drawbacks of the technology include high power consumption and long warm-up times from a cold state.
Also, some users complain that the resulting prints are difficult to write on (the wax tends to repel inks from pens), and are difficult to feed through Automatic Document Feeders, but these traits have been significantly reduced in later models. In addition, this type of printer is only available from one manufacturer, Xerox, manufactured as part of their Xerox Phaser office printer line is also available by various Xerox concessionaires[2].[3] Previously, solid ink printers were manufactured by Tektronix, but Tek sold the printing business to Xerox in 2001.
[edit] Dye-sublimation printers
Main article: Dye-sublimation printer
A dye-sublimation printer (or dye-sub printer) is a printer which employs a printing process that uses heat to transfer dye to a medium such as a plastic card, paper or canvas. The process is usually to lay one color at a time using a ribbon that has color panels. Dye-sub printers are intended primarily for high-quality color applications, including color photography; and are less well-suited for text. While once the province of high-end print shops, dye-sublimation printers are now increasingly used as dedicated consumer photo printers.
[edit] Inkless printers
[edit] Thermal printers
Main article: Thermal printer
Thermal printers work by selectively heating regions of special heat-sensitive paper. Monochrome thermal printers are used in cash registers, ATMs, gasoline dispensers and some older inexpensive fax machines. Colors can be achieved with special papers and different temperatures and heating rates for different colors. One example is the ZINK technology.
[edit] UV printers
Xerox is working on an inkless printer which will use a special reusable paper coated with a few micrometres of UV light sensitive chemicals. The printer will use a special UV light bar which will be able to write and erase the paper. As of early 2007 this technology is still in development and the text on the printed pages can only last between 16–24 hours before fading.[4]
[edit] Obsolete and special-purpose printing technologies
The following technologies are either obsolete, or limited to special applications though most were, at one time, in widespread use.
Impact printers rely on a forcible impact to transfer ink to the media, similar to the action of a typewriter. All but the dot matrix printer rely on the use of formed characters, letterforms that represent each of the characters that the printer was capable of printing. In addition, most of these printers were limited to monochrome printing in a single typeface at one time, although bolding and underlining of text could be done by overstriking, that is, printing two or more impressions in the same character position. Impact printers varieties include, Typewriter-derived printers, Teletypewriter-derived printers, Daisy wheel printers, Dot matrix printers and Line printers. Dot matrix printers remain in common use in businesses where multi-part forms are printed, such as car rental service counters. An overview of impact printing [5] contains a detailed description of many of the technologies used.
Pen-based plotters were an alternate printing technology once common in engineering and architectural firms. Pen-based plotters rely on contact with the paper (but not impact, per se), and special purpose pens that are mechanically run over the paper to create text and images.
[edit] Typewriter-derived printers
Main articles: Friden Flexowriter and IBM Selectric typewriter
Several different computer printers were simply computer-controllable versions of existing electric typewriters. The Friden Flexowriter and IBM Selectric typewriter were the most-common examples. The Flexowriter printed with a conventional typebar mechanism while the Selectric used IBM's well-known "golf ball" printing mechanism. In either case, the letter form then struck a ribbon which was pressed against the paper, printing one character at a time. The maximum speed of the Selectric printer (the faster of the two) was 15.5 characters per second.
[edit] Teletypewriter-derived printers
Main article: Teleprinter
The common teleprinter could easily be interfaced to the computer and became very popular except for those computers manufactured by IBM. Some models used a "typebox" that was positioned (in the X- and Y-axes) by a mechanism and the selected letter from was struck by a hammer. Others used a type cylinder in a similar way as the Selectric typewriters used their type ball. In either case, the letter form then struck a ribbon to print the letterform. Most teleprinters operated at ten characters per second although a few achieved 15 CPS.
[edit] Daisy wheel printers
Main article: Daisy wheel printer
Daisy-wheel printers operate in much the same fashion as a typewriter. A hammer strikes a wheel with petals (the daisy wheel), each petal containing a letter form at its tip. The letter form strikes a ribbon of ink, depositing the ink on the page and thus printing a character. By rotating the daisy wheel, different characters are selected for printing.
These printers were also referred to as letter-quality printers because, during their heyday, they could produce text which was as clear and crisp as a typewriter (though they were nowhere near the quality of printing presses). The fastest letter-quality printers printed at 30 characters per second.
[edit] Dot-matrix printers
Main article: Dot matrix printer
In the general sense many printers rely on a matrix of pixels, or dots, that together form the larger image. However, the term dot matrix printer is specifically used for impact printers that use a matrix of small pins to create precise dots. The advantage of dot-matrix over other impact printers is that they can produce graphical images in addition to text; however the text is generally of poorer quality than impact printers that use letterforms (type).
A Tandy 1000 HX with a Tandy DMP-133 dot-matrix printer.
Dot-matrix printers can be broadly divided into two major classes:
• Ballistic wire printers (discussed in the dot matrix printers article)
• Stored energy printers
Dot matrix printers can either be character-based or line-based (that is, a single horizontal series of pixels across the page), referring to the configuration of the print head.
At one time, dot matrix printers were one of the more common types of printers used for general use — such as for home and small office use. Such printers would have either 9 or 24 pins on the print head. 24-pin print heads were able to print at a higher quality. Once the price of inkjet printers dropped to the point where they were competitive with dot matrix printers, dot matrix printers began to fall out of favor for general use.
Some dot matrix printers, such as the NEC P6300, can be upgraded to print in color. This is achieved through the use of a four-color ribbon mounted on a mechanism (provided in an upgrade kit that replaces the standard black ribbon mechanism after installation) that raises and lowers the ribbons as needed. Color graphics are generally printed in four passes at standard resolution, thus slowing down printing considerably. As a result, color graphics can take up to four times longer to print than standard monochrome graphics, or up to 8-16 times as long at high resolution mode.
Dot matrix printers are still commonly used in low-cost, low-quality applications like cash registers, or in demanding, very high volume applications like invoice printing. The fact that they use an impact printing method allows them to be used to print multi-part documents using carbonless copy paper (like sales invoices and credit card receipts), whereas other printing methods are unusable with paper of this type. Dot-matrix printers are now (as of 2005) rapidly being superseded even as receipt printers.
[edit] Line printers
Main article: Line printer
Line printers, as the name implies, print an entire line of text at a time. Three principal designs existed. In drum printers, a drum carries the entire character set of the printer repeated in each column that is to be printed. In chain printers (also known as train printers), the character set is arranged multiple times around a chain that travels horizontally past the print line. In either case, to print a line, precisely timed hammers strike against the back of the paper at the exact moment that the correct character to be printed is passing in front of the paper. The paper presses forward against a ribbon which then presses against the character form and the impression of the character form is printed onto the paper.
Comb printers represent the third major design. These printers were a hybrid of dot matrix printing and line printing. In these printers, a comb of hammers printed a portion of a row of pixels at one time (for example, every eighth pixel). By shifting the comb back and forth slightly, the entire pixel row could be printed (continuing the example, in just eight cycles). The paper then advanced and the next pixel row was printed. Because far less motion was involved than in a conventional dot matrix printer, these printers were very fast compared to dot matrix printers and were competitive in speed with formed-character line printers while also being able to print dot-matrix graphics.
Line printers were the fastest of all impact printers and were used for bulk printing in large computer centres. They were virtually never used with personal computers and have now been replaced by high-speed laser printers.
Line printers, better known as linematrix printers are widely used in the automotive, logistic and banking world for high speed and barcode printing. They are known as robust and durable printers that have the lowest price per page (form). Companies as Printronix Inc. and TallyGenicom are the leading manufactures today.
The legacy of line printers lives on in many computer operating systems, which use the abbreviations "lp", "lpr", or "LPT" to refer to printers.
[edit] Pen-based plotters
Main article: Plotter
A plotter is a vector graphics printing device which operates by moving a pen over the surface of paper. Plotters have been (and still are) used in applications such as computer-aided design, though they are being replaced with wide-format conventional printers (which nowadays have sufficient resolution to render high-quality vector graphics using a rasterized print engine). It is commonplace to refer to such wide-format printers as "plotters", even though such usage is technically incorrect.
[edit] Sales
Since 2005, the world's top selling brand of inkjet and laser printers has been HP which now has 46% of sales in inkjet and 50.5% in laser printers. [3]
[edit] Other printers
A number of other sorts of printers are important for historical reasons, or for special purpose uses:
• Digital minilab (photographic paper)
• Electrolytic printers
• Spark printer
• Barcode printer multiple technologies, including: thermal printing, inkjet printing, and laser printing barcodes
• Billboard / sign paint spray printers
• Laser etching (product packaging) industrial printers
• Microsphere (special paper)
[edit] Printing mode
The data received by a printer may be:
1. a string of characters
2. a bitmapped image
3. a vector image
Some printers can process all three types of data, others not.
• Character Printers (such as Daisy wheel printers) can handle only plain text data or rather simple point plots.
• Pen Plotters typically process vector images. Inkjet based Plotters can adequately reproduce all three.
• Modern printing technology, such as laser printers and inkjet printers, can adequately reproduce all three. This is especially true of printers equipped with support for PostScript and/or PCL; which includes the vast majority of printers produced today.
Today it is common to print everything (even plain text) by sending ready bitmapped images to the printer, because it allows better control over formatting. Many printer drivers do not use the text mode at all, even if the printer is capable of it.
[edit] Monochrome, color and photo printers
Main article: Photo printer
A monochrome printer can only produce an image consisting of one color, usually black. A monochrome printer may also be able to produce various tones of that color, such as a grey-scale.
A color printer can produce images of multiple colors.
A photo printer is a color printer that can produce images that mimic the color range (gamut) and resolution of photographic methods of printing. Many can be used autonomously (without a computer), with a memory card or USB connector.
[edit] The printer manufacturing business
Often the razor and blades business model is applied. That is, a company may sell a printer at cost, and make profits on the ink cartridge, paper, or some other replacement part. This has caused legal disputes regarding the right of companies other than the printer manufacturer to sell compatible ink cartridges. To protect the razor and blades business model several manufacturers invest heavily in developing new cartridge technology and patenting it.
Other manufacturers, in reaction to the challenges from using this business model, choose to make more money on printers and less on the ink, promoting the latter through their advertising campaigns. Finally, this generates two clearly different proposals: "cheap printer — expensive ink" or "expensive printer — cheap ink". Ultimately, the consumer decision depends on their reference interest rate or their time preference. From an Economics viewpoint, there is a clear trade-off between cost per copy and cost of the printer[6].
[edit] Printing speed
The speed of early printers was measured in units of characters per second. More modern printers are measured in pages per minute. These measures are used primarily as a marketing tool, and are not well standardised. Usually pages per minute refers to sparse monochrome office documents, rather than dense pictures which usually print much more slowly. PPM are most of the time referring to A4 paper in Europe and Letter (paper size) paper in the US, resulting in a 5-10% difference.
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A Lexmark printer
In computing, a printer is a peripheral which produces a hard copy (permanent readable text and/or graphics) of documents stored in electronic form, usually on physical print media such as paper or transparencies. Many printers are primarily used as local peripherals, and are attached by a printer cable or, in most newer printers, a USB cable to a computer which serves as a document source. Some printers, commonly known as network printers, have built-in network interfaces (typically wireless and/or Ethernet), and can serve as a hardcopy device for any user on the network. Individual printers are often designed to support both local and network connected users at the same time. In addition, a few modern printers can directly interface to electronic media such as memory sticks or memory cards, or to image capture devices such as digital cameras, scanners; some printers are combined with a scanners and/or fax machines in a single unit, and can function as photocopiers. Printers that include non-printing features are sometimes called Multifunction printers (MFP), Multi-Function Devices (MFD), or All-In-One (AIO) printers. Most MFPs include printing, scanning, and copying among their features.
A Virtual printer is a piece of computer software whose user interface and API resemble that of a printer driver, but which is not connected with a physical computer printer.
Printers are designed for low-volume, short-turnaround print jobs; requiring virtually no setup time to achieve a hard copy of a given document. However, printers are generally slow devices (30 pages per minute is considered fast; and many inexpensive consumer printers are far slower than that), and the cost per page is actually relatively high. However this is offset by the on-demand convenience and project management costs being more controllable compared to an out-sourced solution. The printing press naturally remains the machine of choice for high-volume, professional publishing. However, as printers have improved in quality and performance, many jobs which used to be done by professional print shops are now done by users on local printers; see desktop publishing. The world's first computer printer was a 19th century mechanically driven apparatus invented by Charles Babbage for his Difference Engine.[1]
Contents
[hide]
• 1 Printing technology
• 2 Modern print technology
o 2.1 Toner-based printers
o 2.2 Liquid inkjet printers
o 2.3 Solid ink printers
o 2.4 Dye-sublimation printers
o 2.5 Inkless printers
2.5.1 Thermal printers
2.5.2 UV printers
• 3 Obsolete and special-purpose printing technologies
o 3.1 Typewriter-derived printers
o 3.2 Teletypewriter-derived printers
o 3.3 Daisy wheel printers
o 3.4 Dot-matrix printers
o 3.5 Line printers
o 3.6 Pen-based plotters
• 4 Sales
• 5 Other printers
• 6 Printing mode
• 7 Monochrome, color and photo printers
• 8 The printer manufacturing business
• 9 Printing speed
• 10 See also
• 11 References
[edit] Printing technology
Printers are routinely classified by the underlying print technology they employ; numerous such technologies have been developed over the years. The choice of print engine has a substantial effect on what jobs a printer is suitable for, as different technologies are capable of different levels of image/text quality, print speed, low cost, noise; in addition, some technologies are inappropriate for certain types of physical media (such as carbon paper or transparencies).
Another aspect of printer technology that is often forgotten is resistance to alteration: liquid ink such as from an inkjet head or fabric ribbon becomes absorbed by the paper fibers, so documents printed with a liquid ink sublimation printer are more difficult to alter than documents printed with toner or solid inks, which do not penetrate below the paper surface.
Checks should either be printed with liquid ink or on special "check paper with toner anchorage".[1] For similar reasons carbon film ribbons for IBM Selectric typewriters bore labels warning against using them to type negotiable instruments such as checks. The machine-readable lower portion of a check, however, must be printed using MICR toner or ink. Banks and other clearing houses employ automation equipment that relies on the magnetic flux from these specially printed characters to function properly.
[edit] Modern print technology
The following printing technologies are routinely found in modern printers:
[edit] Toner-based printers
Main article: Laser printer
Toner-based printers work using the Xerographic principle that is used in most photocopiers: by adhering toner to a light-sensitive print drum, then using static electricity to transfer the toner to the printing medium to which it is fused with heat and pressure.
The most common type of toner-based printer is the laser printer, which uses precision lasers to cause toner adherence. Laser printers are known for high quality prints, good print speed, and a low (Black and White) cost-per-copy. They are the most common printer for many general-purpose office applications, but are much less common as consumer printers due to their high initial cost — although this cost is dropping.
Laser printers are available in both color and monochrome varieties.
Another toner based printer is the LED printer which uses an array of LEDs instead of a laser to cause toner adhesion to the print drum.
Recent research has also indicated that Laser printers emit potentially dangerous ultrafine particles, possibly causing health problems associated with respiration [1] and cause pollution equivalent to cigarettes.[2] The degree of particle emissions varies with age, model and design of each printer but is generally proportional to the amount of toner required. Furthermore, a well ventilated workspace would allow such ultrafine particles to disperse thus reducing the health side effects.
[edit] Liquid inkjet printers
Inkjet printers operate by propelling variably-sized droplets of liquid or molten material (ink) onto almost any sized page. They are the most common type of computer printer for the general consumer.
[edit] Solid ink printers
Main article: Solid ink
Solid Ink printers, also known as phase-change printers, are a type of thermal transfer printer. They use solid sticks of CMYK colored ink (similar in consistency to candle wax), which are melted and fed into a piezo crystal operated print-head. The printhead sprays the ink on a rotating, oil coated drum. The paper then passes over the print drum, at which time the image is transferred, or transfixed, to the page.
Solid ink printers are most commonly used as color office printers, and are excellent at printing on transparencies and other non-porous media. Solid ink printers can produce excellent results. Acquisition and operating costs are similar to laser printers. Drawbacks of the technology include high power consumption and long warm-up times from a cold state.
Also, some users complain that the resulting prints are difficult to write on (the wax tends to repel inks from pens), and are difficult to feed through Automatic Document Feeders, but these traits have been significantly reduced in later models. In addition, this type of printer is only available from one manufacturer, Xerox, manufactured as part of their Xerox Phaser office printer line is also available by various Xerox concessionaires[2].[3] Previously, solid ink printers were manufactured by Tektronix, but Tek sold the printing business to Xerox in 2001.
[edit] Dye-sublimation printers
Main article: Dye-sublimation printer
A dye-sublimation printer (or dye-sub printer) is a printer which employs a printing process that uses heat to transfer dye to a medium such as a plastic card, paper or canvas. The process is usually to lay one color at a time using a ribbon that has color panels. Dye-sub printers are intended primarily for high-quality color applications, including color photography; and are less well-suited for text. While once the province of high-end print shops, dye-sublimation printers are now increasingly used as dedicated consumer photo printers.
[edit] Inkless printers
[edit] Thermal printers
Main article: Thermal printer
Thermal printers work by selectively heating regions of special heat-sensitive paper. Monochrome thermal printers are used in cash registers, ATMs, gasoline dispensers and some older inexpensive fax machines. Colors can be achieved with special papers and different temperatures and heating rates for different colors. One example is the ZINK technology.
[edit] UV printers
Xerox is working on an inkless printer which will use a special reusable paper coated with a few micrometres of UV light sensitive chemicals. The printer will use a special UV light bar which will be able to write and erase the paper. As of early 2007 this technology is still in development and the text on the printed pages can only last between 16–24 hours before fading.[4]
[edit] Obsolete and special-purpose printing technologies
The following technologies are either obsolete, or limited to special applications though most were, at one time, in widespread use.
Impact printers rely on a forcible impact to transfer ink to the media, similar to the action of a typewriter. All but the dot matrix printer rely on the use of formed characters, letterforms that represent each of the characters that the printer was capable of printing. In addition, most of these printers were limited to monochrome printing in a single typeface at one time, although bolding and underlining of text could be done by overstriking, that is, printing two or more impressions in the same character position. Impact printers varieties include, Typewriter-derived printers, Teletypewriter-derived printers, Daisy wheel printers, Dot matrix printers and Line printers. Dot matrix printers remain in common use in businesses where multi-part forms are printed, such as car rental service counters. An overview of impact printing [5] contains a detailed description of many of the technologies used.
Pen-based plotters were an alternate printing technology once common in engineering and architectural firms. Pen-based plotters rely on contact with the paper (but not impact, per se), and special purpose pens that are mechanically run over the paper to create text and images.
[edit] Typewriter-derived printers
Main articles: Friden Flexowriter and IBM Selectric typewriter
Several different computer printers were simply computer-controllable versions of existing electric typewriters. The Friden Flexowriter and IBM Selectric typewriter were the most-common examples. The Flexowriter printed with a conventional typebar mechanism while the Selectric used IBM's well-known "golf ball" printing mechanism. In either case, the letter form then struck a ribbon which was pressed against the paper, printing one character at a time. The maximum speed of the Selectric printer (the faster of the two) was 15.5 characters per second.
[edit] Teletypewriter-derived printers
Main article: Teleprinter
The common teleprinter could easily be interfaced to the computer and became very popular except for those computers manufactured by IBM. Some models used a "typebox" that was positioned (in the X- and Y-axes) by a mechanism and the selected letter from was struck by a hammer. Others used a type cylinder in a similar way as the Selectric typewriters used their type ball. In either case, the letter form then struck a ribbon to print the letterform. Most teleprinters operated at ten characters per second although a few achieved 15 CPS.
[edit] Daisy wheel printers
Main article: Daisy wheel printer
Daisy-wheel printers operate in much the same fashion as a typewriter. A hammer strikes a wheel with petals (the daisy wheel), each petal containing a letter form at its tip. The letter form strikes a ribbon of ink, depositing the ink on the page and thus printing a character. By rotating the daisy wheel, different characters are selected for printing.
These printers were also referred to as letter-quality printers because, during their heyday, they could produce text which was as clear and crisp as a typewriter (though they were nowhere near the quality of printing presses). The fastest letter-quality printers printed at 30 characters per second.
[edit] Dot-matrix printers
Main article: Dot matrix printer
In the general sense many printers rely on a matrix of pixels, or dots, that together form the larger image. However, the term dot matrix printer is specifically used for impact printers that use a matrix of small pins to create precise dots. The advantage of dot-matrix over other impact printers is that they can produce graphical images in addition to text; however the text is generally of poorer quality than impact printers that use letterforms (type).
A Tandy 1000 HX with a Tandy DMP-133 dot-matrix printer.
Dot-matrix printers can be broadly divided into two major classes:
• Ballistic wire printers (discussed in the dot matrix printers article)
• Stored energy printers
Dot matrix printers can either be character-based or line-based (that is, a single horizontal series of pixels across the page), referring to the configuration of the print head.
At one time, dot matrix printers were one of the more common types of printers used for general use — such as for home and small office use. Such printers would have either 9 or 24 pins on the print head. 24-pin print heads were able to print at a higher quality. Once the price of inkjet printers dropped to the point where they were competitive with dot matrix printers, dot matrix printers began to fall out of favor for general use.
Some dot matrix printers, such as the NEC P6300, can be upgraded to print in color. This is achieved through the use of a four-color ribbon mounted on a mechanism (provided in an upgrade kit that replaces the standard black ribbon mechanism after installation) that raises and lowers the ribbons as needed. Color graphics are generally printed in four passes at standard resolution, thus slowing down printing considerably. As a result, color graphics can take up to four times longer to print than standard monochrome graphics, or up to 8-16 times as long at high resolution mode.
Dot matrix printers are still commonly used in low-cost, low-quality applications like cash registers, or in demanding, very high volume applications like invoice printing. The fact that they use an impact printing method allows them to be used to print multi-part documents using carbonless copy paper (like sales invoices and credit card receipts), whereas other printing methods are unusable with paper of this type. Dot-matrix printers are now (as of 2005) rapidly being superseded even as receipt printers.
[edit] Line printers
Main article: Line printer
Line printers, as the name implies, print an entire line of text at a time. Three principal designs existed. In drum printers, a drum carries the entire character set of the printer repeated in each column that is to be printed. In chain printers (also known as train printers), the character set is arranged multiple times around a chain that travels horizontally past the print line. In either case, to print a line, precisely timed hammers strike against the back of the paper at the exact moment that the correct character to be printed is passing in front of the paper. The paper presses forward against a ribbon which then presses against the character form and the impression of the character form is printed onto the paper.
Comb printers represent the third major design. These printers were a hybrid of dot matrix printing and line printing. In these printers, a comb of hammers printed a portion of a row of pixels at one time (for example, every eighth pixel). By shifting the comb back and forth slightly, the entire pixel row could be printed (continuing the example, in just eight cycles). The paper then advanced and the next pixel row was printed. Because far less motion was involved than in a conventional dot matrix printer, these printers were very fast compared to dot matrix printers and were competitive in speed with formed-character line printers while also being able to print dot-matrix graphics.
Line printers were the fastest of all impact printers and were used for bulk printing in large computer centres. They were virtually never used with personal computers and have now been replaced by high-speed laser printers.
Line printers, better known as linematrix printers are widely used in the automotive, logistic and banking world for high speed and barcode printing. They are known as robust and durable printers that have the lowest price per page (form). Companies as Printronix Inc. and TallyGenicom are the leading manufactures today.
The legacy of line printers lives on in many computer operating systems, which use the abbreviations "lp", "lpr", or "LPT" to refer to printers.
[edit] Pen-based plotters
Main article: Plotter
A plotter is a vector graphics printing device which operates by moving a pen over the surface of paper. Plotters have been (and still are) used in applications such as computer-aided design, though they are being replaced with wide-format conventional printers (which nowadays have sufficient resolution to render high-quality vector graphics using a rasterized print engine). It is commonplace to refer to such wide-format printers as "plotters", even though such usage is technically incorrect.
[edit] Sales
Since 2005, the world's top selling brand of inkjet and laser printers has been HP which now has 46% of sales in inkjet and 50.5% in laser printers. [3]
[edit] Other printers
A number of other sorts of printers are important for historical reasons, or for special purpose uses:
• Digital minilab (photographic paper)
• Electrolytic printers
• Spark printer
• Barcode printer multiple technologies, including: thermal printing, inkjet printing, and laser printing barcodes
• Billboard / sign paint spray printers
• Laser etching (product packaging) industrial printers
• Microsphere (special paper)
[edit] Printing mode
The data received by a printer may be:
1. a string of characters
2. a bitmapped image
3. a vector image
Some printers can process all three types of data, others not.
• Character Printers (such as Daisy wheel printers) can handle only plain text data or rather simple point plots.
• Pen Plotters typically process vector images. Inkjet based Plotters can adequately reproduce all three.
• Modern printing technology, such as laser printers and inkjet printers, can adequately reproduce all three. This is especially true of printers equipped with support for PostScript and/or PCL; which includes the vast majority of printers produced today.
Today it is common to print everything (even plain text) by sending ready bitmapped images to the printer, because it allows better control over formatting. Many printer drivers do not use the text mode at all, even if the printer is capable of it.
[edit] Monochrome, color and photo printers
Main article: Photo printer
A monochrome printer can only produce an image consisting of one color, usually black. A monochrome printer may also be able to produce various tones of that color, such as a grey-scale.
A color printer can produce images of multiple colors.
A photo printer is a color printer that can produce images that mimic the color range (gamut) and resolution of photographic methods of printing. Many can be used autonomously (without a computer), with a memory card or USB connector.
[edit] The printer manufacturing business
Often the razor and blades business model is applied. That is, a company may sell a printer at cost, and make profits on the ink cartridge, paper, or some other replacement part. This has caused legal disputes regarding the right of companies other than the printer manufacturer to sell compatible ink cartridges. To protect the razor and blades business model several manufacturers invest heavily in developing new cartridge technology and patenting it.
Other manufacturers, in reaction to the challenges from using this business model, choose to make more money on printers and less on the ink, promoting the latter through their advertising campaigns. Finally, this generates two clearly different proposals: "cheap printer — expensive ink" or "expensive printer — cheap ink". Ultimately, the consumer decision depends on their reference interest rate or their time preference. From an Economics viewpoint, there is a clear trade-off between cost per copy and cost of the printer[6].
[edit] Printing speed
The speed of early printers was measured in units of characters per second. More modern printers are measured in pages per minute. These measures are used primarily as a marketing tool, and are not well standardised. Usually pages per minute refers to sparse monochrome office documents, rather than dense pictures which usually print much more slowly. PPM are most of the time referring to A4 paper in Europe and Letter (paper size) paper in the US, resulting in a 5-10% difference.
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