An impact printer is a printing device typically used in conjunction with a computer that allows the relatively rapid and repeatable printing of visual materials. Though most often used in obsolete printers for text, some forms of impact printer, such as dot matrix printers, continue to be used for certain purposes. Replaced by toner-based and inkjet printers in most applications, an impact printer works by literally impacting letters or shapes onto a piece of paper. Similar in function to a traditional typewriter, this process involves needles or letter-shaped heads striking against an ink-soaked ribbon and impacting a sheet of paper on the other side.
Designed to function similarly to old-fashioned typewriters, an impact printer is somewhat simplistic but suffered from many of the same problems that typewriters faced. Users of impact printers had to worry about changing ink ribbons, jammed heads, and the inability for most models to create different typefaces and styles as well as lacking the ability to make images. Bold type fonts and underline could be achieved through overstriking, which is applying two or more impacts to the same region of paper. Since the letters themselves were part of the physical construction of the printer, without changing the heads with the letters on them, a user could not change the style or font of the printed text.
Impact printers also suffered from an inability to print in anything but monochromatic or black. Since the process requires a ribbon that is struck by each head, the same color is used throughout the entire printing process. The advent of toner-based and inkjet printers that use individual cartridges of color and pigment to create the completed image made reliable and affordable color printing much more accessible. Toner-based printers use a laser and electrostatic to apply dry ink to a page, while inkjet printers propel liquid ink directly onto a surface to create an image or text.
Dot matrix printers, which are a particular type of impact printer, allow greater customization of text, and simple image printing as well. Instead of using heads with letters on them, a dot matrix printer uses a small needle to impact ink from the ribbon onto the page in a tiny dot. These dots are combined together, by the eyes and mind of an observer, into small patterns that form letters and images. Similar in appearance to some newspaper images, dot matrix printers are still used in some businesses because the physical impact of the process allows reliable printing of both carbon and carbonless copies.