Apart from such obvious considerations as price and durability of the machine, there are four important characteristics of a printer: quality of output, speed, method of feeding paper, and compatibility with the rest of the computer system.
Some printers produce letter-quality output - so called because their output looks as good as that provided by a high-quality typewriter. The most popular type of letter-quality printer is the laser printer. Ink jet printers generate output that is considered to be of slightly lower quality than that of laser printers. The most common type of non-letter-quality printer is the dot-matrix printer, which produces letters by placing a series of tightly clustered dots on a piece of paper to resemble a character. Since there are tiny spaces between the dots, the dot-matrix output does not resemble typed output as closely as does laser or ink jet output.
Color printers have become increasingly abundant. Their shortcomings are (1) it costs about five times as much to print in color as in black ink and (2) the printing process is much slower. Many computer labs work efficiently with one color printer and several regular printers.
Many users purchase a dot-matrix printer simply because this option is cheaper. Others decide to go first class and opt for a laser printer, so that their output will look nicer. However, using improved appearance as the sole criterion for selection is sometimes misleading. The strength of the laser printer is printing multiple copies of high quality output quietly and rapidly. These advantages are gained at the cost of greater expense: laser printers cost three to five times as much as dot-matrix printers to print each page. By slowing down the speed of the dot-matrix printer, it is possible to produce attractive output that is nearly letter quality. The convenience and cost of a dot-matrix printer may outweigh slight losses in appearance. Most users need extremely high quality for only a small portion of their work, and they may feel frustrated to have to produce rough drafts and ordinary output at greater expense.
A common compromise for schools with several printers is to purchase several dot-matrix printers and a single laser printer. Rough drafts and ordinary work can be done on the dot-matrix printers, while the laser printer can be reserved for special work. Even among dot-matrix printers, there may be a wide range in letter quality. It is therefore essential to examine a sample of the machine's output before purchasing a printer.
The speed at which printers print varies widely. The manuscript for the first edition of this book took a little over a minute per page to print in letter quality on a dot-matrix printer. The current edition printed on a laser printer at the rate of 16 pages per minute. Faster printers cost more money, but the reduction in backlog requiring students to wait for slower printers may justify the additional expense.
Dot-matrix printers require special form-feed paper. Laser and ink-jet printers work well with ordinary paper. This means that with laser printers you can print envelopes, print on letterhead stationery, and even print on both sides of the paper (by feeding it through the printer a second time).
Be sure to determine whether a printer will be compatible with your computer and with the software you plan to run on it. Some programs, for example, generate attractive print fonts on laser printers, but to do this they employ a technique called PostScript, which is not available with all laser printers. (If the computer doesn't have PostScript capabilities, the output reverts to a more ordinary print font.) Furthermore, most printers must be connected to the CPU with a special cable (and sometimes an interface card) and must have software (called a print driver) that is appropriate for that unique combination of computer and printer. The interface card, cable, or print driver for some off-brand printers and computers may be hard to find, expensive, or difficult to maintain.
While the computer is sending output to the printer, it may temporarily be impossible to use the computer system to do anything else. Since printing is a slow procedure, other valuable work may simply come to a halt while the user waits for the printer to complete its task. One way to minimize this delay is to add a printer buffer to your system. When it receives instructions to send output to the printer, the computer immediately sends the output to the buffer, perhaps at the rate of several pages per second. The buffer then releases the information to the printer at the speed the printer can handle, perhaps at the rate of 15 seconds per page. Meanwhile the rest of the computer system is immediately free to perform nonprinting tasks. Buffers come in various sizes. A 32K buffer will hold 32,000 characters, which amounts to about 32 double-spaced pages; a 1 MB buffer would hold a much larger number of pages.
When printers are part of a LAN, a buffer (in this case, called a spooler) is almost a necessity. Users at several computers can send work to be printed to the spooler and then continue with other work, while their output waits its turn to be printed. Without a spooler, users would have to engage in the wasteful, non-technological activity of looking around the room and waiting to see when the printer became available in order to print their output.