Years ago computers were huge and their accompanying printers were huge as well. Instead of ink cartridges like those used now, they had toner reservoirs and later toner cartridges. Filling a toner cartridge was not easy and it was messy. The toner cartridges were better. Some printers ran on print wheels and some used ribbons.
Now our computers are more compact and printers do more than just print in some cases. Printers use cartridges with self-contained reservoirs. Some can be refilled and it isn't as messy as adding toner was.
There are two types of printer cartridges. Primarily Hewlett-Packard and Epson printers use first, Piezo Electric. A small crystal is subjected to an electric current that causes crystal to expand about every 5 microseconds (20,000 per second. This expansion causes inkjet ink to be squirted out through print heads very rapidly and precisely. Piezo Electric has fewer print heads than bubble jet/thermal printers but can do more precise action and tend to last longer.
Bubble jet print cartridges heat ink rapidly into a bubble and is squirted through ink nozzles thousands of times per second. Bubble jet printers are quieter than Piezo based printers. It gives you extremely high resolution color printing.
Ink jet not megapixel method has ink squirted through nozzles as they move over a variety of media. Liquid ink in various colors is squirted at paper to create an image. The print head scans page horizontally using a motor assembly that rolls paper in vertical steps.
A strip of an image is printed, then paper moves on ready for next step. For speed, it doesn't just print a strip across page; it prints vertical rows of pixels in each pass.
There are various types of inkjet technology. DOD or drop on demand squirts small drops of in ink onto paper through tiny nozzles. It is like turning a hosepipe on and off 5,000 times per second. The amount of ink dropped on page is controlled by driver software that says which nozzles fire and when. A problem with ink jet technology is tendency for ink to smudge right after printing. This is improving with development of new ink compositions.
Thermal Technology of printing fires ink onto paper. There are three stages in this process. In stage 1 squirt is started when ink is heated to create a bubble. Initial pressure bursts bubble and hits paper. The bubble breaks as heating element cools. The vacuum that is created draws ink from reservoir to replace ink that was ejected.