Print quality is measured in dots per inch (dpi). The more dots, the denser the character or line. A printer capable of at least 250 dpi is called letter quality. Most letter-quality printers print 300 dpi or more.

Print speed usually is measured in pages-per-minute (ppm). Most printers are capable of eight to 12 ppm of black & white text. Graphics take longer than text, and color takes longer than black & white.

A letter-quality printer can print a variety of typesizes and fonts. Basic fonts such as Times Roman and Helvetica are often pre-installed with application software or your OS. Specialty fonts must be installed.

There are several ways a computer forms characters and transfers them to a printer. One popular page-description language is PostScript, which requires a PostScript-compatible printer and PostScript fonts in your computer. Other printer/font standards include True Type and bit-mapped fonts, which do not require corresponding hardware compatibility and are often found in ink jet and low-end laser printers. Most laser printers can be upgraded to PostScript.

Like other peripherals, printers designed for Macintosh computers generally are not compatible with IBM-compatible machines.

Variations

Printers are divided into categories based on technology: dot matrix, ink jet and laser. Printers may print in black only or in full color.

A dot matrix printer uses small pins to strike a ribbon and form characters. The more pins you have (from nine to 24) the better the quality of output. The dot matrix element moves across a page and forms lines at a time, rather than printing a character at a time. Most dot matrix printers produce graphics as well as print, but they are the lowest-quality printer, rarely surpassing 200 dpi.

The most popular inexpensive printers are ink jet. Ink jet printers spray finely tuned shots of ink on a page to form characters. Ink jet printers may require specially coated paper that keeps the ink from blotting. An ink jet printer capable of 300 dpi and higher output is a good choice for the user on a budget.

The highest-quality and most flexible printer is the laser printer, which transfers images to a page like a photocopier. A laser beam etches an image on a photosensitive drum coated with toner. A charged sheet of paper rolls against the drum, and the image is transferred to the paper. The page is then heated to fuse the toner to the paper.

A laser printer is capable of at least 300 dpi, usually much more. Rather than printing character by character or line by line, a laser printer prints an entire page at a time.

A special type of printer used in engineering and architectural applications is called a plotter. A plotter has pens that render precise drawings, such as blueprints or presentation graphics, created with graphics or computer-aided design (CAD) software.

Phototypesetting is available for applications such as book and magazine publishing via linotype printer. These expensive printers are capable of 1,250 dpi and higher; service bureaus sell linotype output for a per-page fee.

All printers consume supplies. Inked ribbons must be replaced in matrix printers. Ink jet cartridges must be changed when empty. Laser printers use toner cartridges. These cartridges usually produce 2,500 to 4,000 pages before they need to be replaced. Many cartridges are reusable and can be refilled with toner rather than completely replaced.

Purchase

Your printer choice depends on whether you need business letters or camera-ready copy and how much printing you do. Buy a printer that supports the software you work with.

Most printers come with a power cord but not a cable for connection to the computer. If a cable is not packaged with your printer, consider the length you'll need as well as the proper connectors.

If you need to print musical notation, mathematical symbols, foreign languages, or special print styles, be sure the printer you select can print them.

Accessories

Printers increasingly are being used to print out pictures from the Internet or digital cameras. Standard bond paper is often inadequate for reproducing these images, especially when using an ink jet printer. With specialty glossy-finish, photo-like paper, even the simplest color ink jet printer can produce startling results.

Printer manufacturers may imply that you can use only their papers with their printers, but you can use any specialty paper with any brand printer. You do need to match the type of printer - ink jet or laser -to the type of paper.

The dyes used in ink jet are not designed to last long periods. Unlike a photo print, a picture made from your ink jet printer may last only a year or so when framed and exposed to light. Fortunately, you can always reprint the picture if it fades.

Special printer products are available like sheets of mailing labels and clear acetate for creating overhead projections.

Maintenance

Dust is the enemy of a printer even more than with other electronics, since often the operating parts are exposed. The best way to keep your printer in top working order is by using a dust cover.

Ink, correction fluid and other contaminants spell trouble if your printer has a rubber roller, or platen, found on most dot matrix and ink jet printers. Use a special platen cleaner with a preloaded cleaning solution, a soft brush or a lint-free cloth, or a can of compressed air to blow away dust. Clean the platen each time you change your ribbon or cartridge. You will find easy-to-use platen cleaner at office supply stores.

Most printer software contains utilities that enable you to perform periodic maintenance, such as clearing the nozzles on ink jet printers and checking ink levels in the cartridges.