Printer

A printer is an output device that turns digital documents and images into marks on a physical medium, most often paper, by depositing ink, fusing toner or applying heat. Where a monitor shows a page for a moment, a printer produces a lasting copy, and the technology that does so determines almost everything about its cost per page, speed, quality and suitability for a task. The three families that matter most today are inkjet, laser and thermal, with older impact printers and newer three-dimensional printers on either side of them.

An inkjet printer forms an image by firing microscopic droplets of liquid ink from nozzles in a moving print head onto the page. The droplets are ejected either by heating a thin film of ink into a vapor bubble that pushes a droplet out, the thermal method used by HP and Canon, or by an electrically driven piezoelectric element that squeezes the nozzle, used by Epson. Four inks, cyan, magenta, yellow and black, are standard, with photo models adding more colors for smoother tones. Inkjets handle color and photographs well and have a low purchase price, but the ink is liquid, so nozzles can clog if the printer sits unused, and water-based ink may smear when wet. The business model of selling cheap printers and expensive cartridges is a common complaint, and the pitfall is judging a printer by its sticker price rather than by cost per page.

A laser printer uses the xerographic process, in which a laser draws an electrostatic image of the page on a rotating drum, and dry toner powder is attracted to the charged areas and fused to the paper. The underlying electrophotography was invented by Chester Carlson in 1938 and commercialized by the company that became Xerox; Gary Starkweather at Xerox, beginning around 1969 and later at PARC, adapted a laser to write the image, and the Xerox 9700 of the late 1970s was an early commercial result. The desktop laser arrived in 1984 with the HP LaserJet, built on a Canon engine. Toner is a fine plastic powder with pigment, not ink, which is why laser output is sharp, fast and water-resistant, and the machines are efficient for large volumes of text. The fuser reaches high temperatures, and the drum and toner are the consumables.

Thermal printers produce an image with heat instead of ink or toner, which makes them simple, quiet and ideal for receipts, shipping labels and tickets. In direct thermal printing, a row of tiny heating elements touches special paper coated with a chemical that darkens when warmed, so there is no ink at all, though the output fades with heat and time. Thermal transfer printing heats a ribbon to melt wax or resin onto labels, producing more durable results, and dye-sublimation printers, common for photo booths, use heat to move dye into a coated medium. Older impact printers, such as the dot-matrix machines that struck a ribbon with a column of pins, survive where multi-part carbon forms are still required. In the same lineage, three-dimensional printing, often shortened to 3D printing, builds objects layer by layer, for example by extruding melted plastic filament as in fused deposition modeling, though it shares only the idea of a computer-controlled deposition head with paper printers.

A printer is itself a small computer, and several misunderstandings follow from forgetting this. It has a processor, memory and firmware, and receives jobs over USB, Ethernet or Wi-Fi, converting them into the print-engine's raster form, which is why a complex page may print slowly while the printer is processing rather than printing. Resolution, quoted in dots per inch, counts dots, not distinguishable detail: a printer must combine many small dots to simulate a shade or color, so a printer rated at 1200 dpi does not render a picture at 1200 pixels per inch. Network printers are also computers on the network, so unpatched firmware and open ports are real security risks. For developers, generating PDFs or label formats such as ZPL for thermal printers is a routine part of invoicing and logistics software.

Read a printer as a machine that moves a digital page onto matter by one of a few physical means, ink droplets, fused toner or heat, each trading purchase price, running cost, speed and durability differently, so that choosing one is really choosing which of those costs matters most for the work being printed.