A computer printer is a computer peripheral device that produces a hard copy (permanent human-readable text and/or graphics, usually on paper) from data stored in a computer connected to it.
The data received by a printer may be:
- a string of characters
- a bitmapped image
- a vector image
Some printers can process all three types of data, others not.
Daisy wheel printers can handle only plain text data or rather simple point plots.
Plotters typically process vector images.
PostScript and PCL printers can combine all three types of data.
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.
Monochrome, color and photo printers
A monochrome printer can only produce an image consisting of one color, usually black. A monochrome printer may also be able to produce graduations of tone 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.
Methods of image creation
The media for most printers is paper, so they are usually classified according to the method of image creation:
Laser printers refer to the method used to adhere toner to the media. The advent of cost-effective, precision lasers has made them the dominant toner-based monochrome printer type for home and office applications.
Ink jet printers
Ink jet printers spray very small, precise amounts (usually a few picolitres) of ink onto the media. For color applications including photo printing, ink jet methods are dominant.
Impact printers rely on a forcible impact to transfer ink to the media, similar to typewriters, that are typically limited to reproducing text. A daisy wheel printer is a specific type of impact printer where the type is carried on a wheel.
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 type-based impact printers.
Some sub-classifications of dot-matrix printers are ballistic wire printers and stored energy printers.
Dot matrix printers can either be character-based or line-based, referring to the configuration of the print head.
Dot matrix printers are still commonly used in low-cost, low-quality applications like cash registers. 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 have been superseded for general computing use.
A number of other sorts of printers are important for historical reasons, or for special purpose uses:
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.
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.
Printer job classes
They are collections of printers. Print jobs sent to a class are forwarded to the first available printer in the class.