A great deal of output can be placed onto computer printouts, although hard copy can become difficult to handle and store as it accumulates. In fact, many executives now complain that they are literally drowning in a sea of computer-generated paperwork.
Printers differ in a number of important respects. One involves the printing technology used, namely whether it is impact or nonimpact.
Another concerns speed of operation. Low-speed printers are capable of outputting only one character at a time, whereas high-speed printers can output either a full line or a full page at a time.
Image Source:ipdsprinter.com
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1. Impact Printers :
Most low-speed printers in use today employ a print head that’s impact, dot-matrix mechanism. Typically, an impact dot-matrix mechanism constructs printed characters by repeatedly activating one or more vertical rows of pins.
Impact dot-matrix printers are usually much faster than solid- font printers; a speed of 100 to 200 characters per second in common. Top- of-the-line impact dot-matrix printers are currently rated at about 700 characters per second.
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The quality of output on dot-matrix devices is often lower than that on solid-font devices. Nonetheless, many relatively inexpensive impact dot- matrix printers are capable of printing very respectable-looking output.
These printers use techniques such as packing as many pins as possible on the print head, over striking by making multiple passes on a line, and blending overstrike dots into previous dots by shifting the paper very slightly.
Top-of-the-line impact dot-matrix printers have 24 pins on their print heads, configured in two 12-pin rows. Generally, these printers can create characters that ar virtually indistinguishable from those produced by solid-font printers.
In the world of impact dot-matrix printing, low-quality output is often referred to as draft-quality printing and presentation- quality output as near-letter quality (NLQ) printing.
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Many impact dot-matrix printers can also be used to produce graphical or color output. Graphical output is possible if the printer supports bit mapping. In the case of printers, this means that each individual pin on the print head may be independently software-controlled.
Although producing graphical output is possible and in fact widely practiced on impact dot- matrix printers, however, it is a relatively slow process and usually causes faster wear on the print head than does text output.
Color output is often possible through a process called dithering. Here a multicolored ribbon is used and, through multiple passes, overstrikes, and imperceptible paper shifts, the printer “mixes” new colors and blends colors right on the paper.
Dithering isn’t elegant, but it often meets the need for color output inexpensively. The software used must support multicolored ribbons in order for one to take advantage of this feature.
2. Nonimpact Printing :
Nonimpact printing, which most often employs dot-matrix characters, does not depend on the impact of metal on paper. In fact, no physical contact at all occurs between the printing mechanism and the paper.
The most popular nonimpact methods today utilize electro thermal, thermal-transfer, ink-jet, laser, and array technologies. In electro thermal printing, characters are burned onto a special paper by heated rods on a print head.
Electro thermal printers are available at a very low cost, but they have the disadvantages of requiring special paper (which some people find unpleasant to touch) and being unable to produce color output.
Thermal-transfer printers, which represent a relatively new technology, thermally transfer ink from a wax- based ribbon onto plain paper. These printers can produce output that rivals a daisywheel’s and, because they use a dot-matrix print head, can support high-quality graphics as well.
In addition, thermal-transfer printers can produce overheads for use at meetings.
Ink-jet printers spray small dots of electrically charged ink onto a page to form images. Many models hold several color cartridge: simultaneously, so they are excellent for producing color output. Ink-jet printers are flexible enough to be used as plotters.
Laser printer form images by charging thousands of does on a platen with
a very-high-intensity laser beam.
Then, as with photocopiers, toner is affixed to the charged positions and, when paper is pressed against the platen, an image is formed. Laser printers produce high-resolution text and graphics quickly, but they are usually more expensive than other types of printers.
Array printers, which first became available in 1985, have many of the same properties as laser printers. They contain fewer moving parts, however, so they are more reliable. They are also more expensive.
Impact versus Nonimpact Printers :
There are many important practical differences between impact and nonimpact printers. For one, because nonimpact printers contain fewer moving parts, they generally are much faster and subject to fewer breakdowns.
In addition, because they don’t use hammers, nonimpact printers are quiet. But unless you require very high speeds or high-quality color, these printer are often an expensive alternative.
Furthermore, because most nonimpact printers are dot-matrix devices, they generally can’t match the letter-quality output produced by impact, solid-font printers.