Daisy wheel printing
A daisy wheel printer is a type of computer printer that produces high-quality type, and was often referred to during the 1980s as a letter-quality printer (in contrast to high-quality dot matrix printers, capable of so-called near letter quality (NLQ) output). There were also, and still are, daisy wheel typewriters, based on the same principle.
The system used a small wheel with each letter printed on it in raised metal or plastic. The printer turns the wheel to line up the proper letter under a single pawl which then strikes the back of the letter and drives it into the paper. In many respects the daisy wheel is similar to a standard typewriter in the way it forms its letters on the page, differing only in the details of the mechanism (daisy wheel vs. typebars or the typeball used on IBM Selectric typewriters).
As with daisy wheel typewriters and typeball-based Selectrics, different fonts could be supported through replacing the daisy wheel. Appropriately-written software would stop the printer at the font change, space to the center of the carriage, and prompt the user to change the wheel before proceeding. The Xerox Diablo D25 included this functionality in the printer's hardware. While practical for most needs, a document which alternated frequently between italics and plain text would become an arduous task.
Bold face could typically be supported, though found mostly on later and high-end daisywheel printers. When instructed to print in bold, some printers would double or triple strike a given character, and some servo-based printers would very slightly advance the carriage for a wider (and therefore blacker) character. Still others (typically inexpensive daisy wheel printers) would perform a carriage return (without a line feed) to return to the beginning of the line, space through all non-bold text, and restrike each bolded character - the inherent imprecision in attempting to restrike on exactly the same spot after a carriage return providing the same effect as a far more expensive servo-based printer, though with the unique consequence that as the printer aged, bold text would become bolder.
Daisy wheel printers were fairly common in the 1980s, but were always less popular than dot matrix printers (ballistic wire printers) due to higher cost and the dot-matrix's ability to print graphics and different fonts. Most dot-matrix printers were also substantially faster than competing daisy wheel printers, as each character required that the wheel be rotated to a new position.
As with all other impact printers, daisy wheel printers are loud. Unlike the more familiar whine of a dot-matrix printer, a high speed daisy wheel printer sounded like intermittent machine gun fire.
With the introduction of high-quality laser printers and inkjet printers in the later 1980s, daisy wheel systems quickly disappeared but for the small remaining typewriter market.
Some remaining daisy wheel printers are used by aficionados for line-based (as opposed to page-based) text like logging data, while others use them to print high-quality labels. Both are tasks for which a laser or inkjet printer aren't well suited. Laser printers are page (not line) printers, meaning that they cannot print a line of text without ejecting a full page. As with dot-matrix printers, laser and inkjet printers are also highly vulnerable to damage when printing labels.