Editing Printer (computing) (section)

=====Line printers=====
{{main|Line printer}}
Line printers print an entire line of text at a time. Four principal designs exist.
[[File:Drum-printer.jpg|thumb|left|Print drum from drum printer]]
* '' Drum printers'', where a horizontally mounted rotating drum carries the entire character set of the printer repeated in each printable character position.  The [[IBM 1132]] printer is an example of a drum printer.<ref>{{cite web|archive-date=2022-10-09|archive-url=https://ghostarchive.org/archive/20221009/https://www.cs.auckland.ac.nz/~alan/courses/r&rtc/773notes/01.0.1p.pdf|quote=drum. 120 print wheels. Hammer. Print wheels. Paper. Ribbon. ... 1132|title=Computer Science 773 Robotics and Real-time Control THE IBM 1132|url=https://www.cs.auckland.ac.nz/~alan/courses/r&rtc/773notes/01.0.1p.pdf|url-status=live}}</ref> Drum printers are also found in adding machines and other numeric printers (POS), the dimensions are compact as only a dozen characters need to be supported.<ref>{{cite web|access-date=22 February 2015|archive-date=26 March 2015|archive-url=https://web.archive.org/web/20150326180608/http://www.johnwolff.id.au/calculators/Tech/Logos240/Logos240.htm|author=John Wolff|publisher=John Wolff's Web Museum|title=The Olivetti Logos 240 Electronic Calculator - Technical Description|url=http://www.johnwolff.id.au/calculators/Tech/Logos240/Logos240.htm|url-status=live}}</ref>

[[File:PrinterIBM1403 090325.jpg|thumb|IBM 1403 line printer]]
* ''Chain or train printers'', where the character set is arranged multiple times around a linked chain or a set of character slugs in a track traveling horizontally past the print line.  The [[IBM 1403]] is perhaps the most popular and comes in both chain and train varieties.  The ''band printer'' is a later variant where the characters are embossed on a flexible steel band.  The LP27 from Digital Equipment Corporation is a band printer.
* ''Bar printers'', where the character set is attached to a solid bar that moves horizontally along the print line, such as the [[IBM 1443]].<ref>{{cite book|last=IBM Corporation|title=IBM 1443 PRINTER for 1620/1710 Systems|url=http://bitsavers.informatik.uni-stuttgart.de/pdf/ibm/1620/A26-5730-2_1443_printer_for_1620.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://bitsavers.informatik.uni-stuttgart.de/pdf/ibm/1620/A26-5730-2_1443_printer_for_1620.pdf |archive-date=2022-10-09 |url-status=live}}</ref>
* A fourth design, used mainly on very early printers such as the IBM 402, features independent type bars, one for each printable position. Each bar contains the character set to be printed.  The bars move vertically to position the character to be printed in front of the print hammer.<ref>{{cite book|last=IBM Corporation|title=IBM 402, 403 and 419 Accounting Machines Manual of Operation|year=1963|url=http://bitsavers.informatik.uni-stuttgart.de/pdf/ibm/punchedCard/AccountingMachine/224-1614-13_402-403-419.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://bitsavers.informatik.uni-stuttgart.de/pdf/ibm/punchedCard/AccountingMachine/224-1614-13_402-403-419.pdf |archive-date=2022-10-09 |url-status=live}}</ref>

In each case, to print a line, precisely 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 against a ribbon which then presses against the character form and the impression of the character form is printed onto the paper.  Each system could have slight timing issues, which could cause minor misalignment of the resulting printed characters.  For drum or typebar printers, this appeared as vertical misalignment, with characters being printed slightly above or below the rest of the line.  In chain or bar printers, the misalignment was horizontal, with printed characters being crowded closer together or farther apart.  This was much less noticeable to human vision than vertical misalignment, where characters seemed to bounce up and down in the line, so they were considered as higher quality print.
* ''Comb printers'', also called ''[[line matrix printer]]s'', represent the fifth major design. These printers are a hybrid of [[dot matrix printing]] and line printing. In these printers, a comb of hammers prints a portion of a row of pixels at one time, such as every eighth pixel. By shifting the comb back and forth slightly, the entire pixel row can be printed, continuing the example, in just eight cycles. The paper then advances, and the next pixel row is printed. Because far less motion is involved than in a conventional dot matrix printer, these printers are very fast compared to dot matrix printers and are competitive in speed with formed-character line printers while also being able to print dot matrix graphics.  The [[Printronix]] P7000  series of line matrix printers are still manufactured as of 2013.

Line printers are the fastest of all impact printers and are used for bulk printing in large computer centres. A line printer can print at 1100 lines per minute or faster, frequently printing pages more rapidly than many current laser printers.  On the other hand, the mechanical components of line printers operate with tight tolerances and require regular [[preventive maintenance]] (PM) to produce a top quality print. They are virtually never used with [[personal computer]]s and have now been replaced by high-speed [[Laser printing|laser printer]]s.  The legacy of line printers lives on in many [[operating system]]s, which use the abbreviations "lp", "lpr", or "LPT" to refer to printers.