printer.........

A computer printer, or more commonly just a printer, is a device that produces a hard copy (permanent human-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 computer peripherals, and are permanently attached by a printer cable to a computer which serves as a document source. Other printers, commonly known as network printers, have built-in network interfaces (typically wireless or Ethernet), and can serve as a hardcopy device for any user on the network.
In addition, many 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.
A printer which is combined with a scanner can essentially function as a photocopier.
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 (10 pages per minute is considered fast; and many consumer printers are far slower than that), and the cost-per-page is relatively high.
In contrast, the printing press (which serves much the same function), is designed and optimized for high-volume print jobs such as newspaper print runs--printing presses are capable of hundreds of pages per minute or more, and have an incremental cost-per-page which is a fraction of that of printers.
The printing press 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.

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An Epson inkjet printer

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 liquid ink are more difficult to alter than documents printed with toner or solid inks, which do not penetrate below the paper surface.
According to the website of security expert Frank Abagnale 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.

中國早在十一世紀宋朝就由畢昇發明活版印刷術，是為濕式印刷術，亦即需要使用油墨的方式印在紙上；西方的第一本活版印刷術則出現在一四五六年由德國人吉廷堡（Gutenberg）印製的《聖經》。
自此活版印刷術沿用近千年。直到到了十九世紀末至二十世紀初期，複印技術才開始進入萌芽階段；文件的複印主要用攝影方式、藍圖法和重氮法。這些方式必須使用化學藥劑，不但藥水味濃厚，且由於濕式顯像的關係，翻印的文字模糊又不能持久，只要放上一段時間，隨著化學藥劑的裂解與揮發，複本上的的字體也會跟著變黃、變淡，最後終於揮發消失掉。
直到二十世紀中期，乾式印刷才被發明出來；到了70年代，半導體技術萌芽，助長了乾式印刷術的技術提昇，造紙技術越臻成熟列印品質越趨穩定，才漸漸打開市場；到90年代電腦普及資訊技術一日千里，由乾式印刷術為基礎的影印機與雷射印表機才漸漸普及。