A dot matrix printer or impact matrix printer that widely used as in office equipment refers to a type of computer printer with a print head that runs back and forth on the page and prints by impact, striking an ink-soaked cloth printer ribbon against the paper, much like a typewriter.

Unlike a typewriter or daisy wheel printer, letters are drawn out of a dot matrix, and thus, varied fonts and arbitrary graphics can be produced. Because the printing involves mechanical pressure, these printers can create carbon copies and carbonless copies.

Each dot is produced by a tiny metal rod, also called a "wire" or "pin", which is driven forward by the power of a tiny electromagnet or solenoid, either directly or through small levers (pawls). Facing the ribbon and the paper is a small guide plate (often made of an artificial jewel such as sapphire or ruby) pierced with holes to serve as guides for the pins.

The moving portion of the printer is called the print head, and when running the printer as a generic text device generally prints one line of text at a time. Most dot matrix printers have a single vertical line of dot-making equipment on their print heads; others have a few interleaved rows in order to improve dot density.

These printing machines can be highly durable as office equipment or small business usage. When they do wear out, it is generally due to ink invading the guide plate of the print head, causing grit to adhere to it; this grit slowly causes the channels in the guide plate to wear from circles into ovals or slots, providing less and less accurate guidance to the printing wires. Eventually, even with tungsten blocks and titanium pawls, the printing becomes too unclear to read. Although nearly all inkjet, thermal, and laser printers produce dot matrices, in common parlance these are seldom called "dot matrix" printers, to avoid confusion with dot matrix impact printers.

Industrial market
Industrial-market printers are designed for high-volume printing and offer construction, feed paths, and carriage configurations suited for this task. The carriage assembly typically houses multiple printheads, permitting rapid printing of the entire paper-width with only a partial carriage displacement. Industrial printers are often cabinet-sized, with their own housing for blank paper, the printer, and printed output. Suppliers of industrial impact printers include Mannesmann-Tally, PSi, Genicom and Printronix.

Personal computer market
In the 1970s and 1980s, dot matrix impact printers were generally considered the best combination of expense and versatility, and until the 1990s they were by far the most common form of printer used with personal computers. The Epson MX-80 was the groundbreaking model that sparked the initial popularity of impact printers in the personal computer market. The MX-80 combined affordability with solid text output (for its time.) Early impact printers (including the MX) were notoriously loud during operation, a result of the hammer-like mechanism in the print head. Furthermore, the MX-80's low dot density (60dpi horizontal, 72dpi vertical) produced printouts of a distinctive "computerized" quality.

When compared to the crisp typewriter quality of a daisy-wheel printer, the dot-matrix printer's legibility appeared especially bad. In office applications, output quality was a serious issue, as the dot-matrix text's readability would rapidly degrade with each photocopy generation.

Progressive hardware improvements to impact printers boosted the carriage speed, added more (typeface) font options, increased the dot density (from 60dpi up to 240dpi), and added pseudo-color printing. Faster carriage speeds meant faster (and sometimes louder) printing. Additional typefaces allowed the user to vary the text appearance of printouts. Proportional-spaced fonts allowed the printer to imitate the non-uniform character widths of a typesetter. Increased dot density allowed for more detailed, darker printouts.

The impact pins of the printhead were constrained to a minimum size (for structural durability), and dot densities above 100dpi merely caused adjacent dots to overlap. While the pin diameter placed a lower limit on the smallest reproducible graphic detail, manufacturers were able to use higher dot density to great effect in improving text quality.Several dot-matrix impact printers (such as the Epson FX series) offered 'user-downloadable fonts'. This gave the user the flexibility to print with different typefaces. PC software downloaded a user-defined fontset into the printer's memory, replacing the built-in typeface with the user's selection.

Any subsequent text printout would use the downloaded font, until the printer was powered off or soft-reset. Several third-party programs were developed to allow easier management of this capability. With a supported word-processor program (such as WordPerfect 5.1), the user could embed up to 2 NLQ custom typefaces in addition to the printer's built-in (ROM) typefaces. (The later rise of WYSIWYG software philosophy rendered downloaded fonts obsolete). Single-strike and Multi-strike ribbons were an attempt to address issues in the ribbon's ink quality.

Standard printer ribbons used the same principles as typewriter ribbons. The printer would be at its darkest with a newly installed ribbon cartridge, but would gradually grow fainter with each successive printout. The variation in darkness over the ribbon cartridge's lifetime prompted the introduction of alternative ribbon formulations. Single-strike ribbons used a carbon-like substance in typewriter ribbons transfer. As the ribbon was only usable for a single loop (rated in terms of 'character count'), the blackness was of consistent, outstanding darkness. Multi-strike ribbons gave an increase in ribbon life, at the expense of quality.

Use of dot matrix printers today
The desktop impact printer was gradually replaced by the inkjet printer. When Hewlett-Packard's patents expired on steam-propelled photolithographically-produced ink-jet heads, the inkjet mechanism became available to the printer industry. The inkjet was superior in nearly all respects: comparatively quiet operation, faster print speed, and output quality almost as good as a laser printer.

Dot matrix printers are also more tolerant of the hot and dirty operating conditions found in many industrial settings. The simplicity and durability of the design allows users who are not "computer literate" to easily perform routine tasks such as changing ribbons and correcting paper jams.Some companies, such as WeP Peripherals, Epson, Okidata, Olivetti, Lexmark, and TallyGenicom, still produce serial and line printers.

Today, a new dot matrix printer actually costs more than most inkjet printers and some entry level laser printers. However, not much should be read into this price difference as the printing costs for inkjet and laser printers are a great deal higher than for dot matrix printers, and the inkjet/laser printer manufacturers effectively use their monopoly over arbitrarily priced printer cartridges to subsidise the initial cost of the printer itself. Dot matrix ribbons are a commodity and are not monopolised by the printer manufacturers themselves.

Dot Matrix Printer Advantages
Dot matrix printers, like any impact printer, can print on multi-part stationery or make carbon copies. Impact printers have one of the lowest printing costs per page.

As the ink is running out, the printout gradually fades rather than suddenly stopping partway through a job. They are able to use continuous paper rather than requiring individual sheets, making them useful for data logging.

They are good, reliable workhorses ideal for use in situations where printed content is more important than quality. The ink ribbon also does not easily dry out, including both the ribbon stored in the casing as well as the portion that is stretched in front of the print head; this unique property allows the dot-matrix printer to be used in environments where printer duty can be rare, for instance, as with a Fire Alarm Control Panel's output.

Dot Matrix Printer Disadvantages
Impact printers are usually noisy, to the extent that sound dampening enclosures are available for use in quiet environments. They can only print low resolution graphics, with limited color performance, limited quality and comparatively low speed. While they support fanfold paper with tractor holes, single-sheet paper usually has to be wound in and aligned by hand, which is relatively inconvenient and time-consuming.

While far better suited to printing on labels than a laser printer or an inkjet printer, they are prone to bent pins (and therefore a destroyed printhead) caused by printing a character half-on and half-off the label; for text-only labels (ie. mailing labels), a daisy wheel printer offers most of the advantages of a dot matrix, with better print quality and a lesser chance of being damaged.

Future of Dot Matrix Printers
The main use of Dot Matrix Printers are in areas of intensive transaction-processing systems that churn out quite a lot of printing. Many companies who might have started off with dot-matrix printers are not so easily convinced to go for printers based on other technologies because of the speed advantage that they have with dot-matrix printers.