Line Printers

Line printers, as the name implies, print an whole line of text at a time. Three principal designs are existed. In drum printers, a drum carries the whole character set of the printer repeated in each column that is to be printed. In chain printers (also called as train printers), the character set is arranged multiple times around a chain that travels horizontally past the print line. In either case, to print a line, specifically timed hammers strike against the back of the paper at the exact moment that the correct character to be printed is passing in front of the paper. The paper presses forward touching a ribbon which then presses against the character form and the impression of the character form is printed onto the paper.

Comb printers characterize the third major design. These printers were a hybrid of dot matrix printing and line printing. In these printers, a comb of hammers printed a part of a row of pixels at one time (for example, every eighth pixel). By shifting the comb back and forth slightly, the complete pixel row could be printed (continuing the example, in just eight cycles). The paper then highly developed and the next pixel row was printed. Because far less motion was involved than in a conservative dot matrix printer, these printers were very fast compared to dot matrix printers and were competitive in speed with formed-character line printers while also being able to print dot-matrix graphics.

Line printers were the fastest of all impact printers and were used for largeness printing in large computer centres. They were almost never used with personal computers and have now been replaced by high-speed laser printers.

The heritage of line printers lives on in many computer operating systems, which use the abbreviations "lp", "lpr", or "LPT" to refer to printers.