page_title: Line printer
section_title: Drum printer
hierarchical_section_title: Line printer / Designs / Timing-sensitive designs / Drum printer
context_page_description: A line printer prints one entire line of text before advancing to another line. Most early line printers were
  impact printers.
  Line printers are mostly associated with unit record equipment and the early days of digital computing, but the technology is still in use. Print speeds of 600 lines per minute were achieved in the 1950s, later increasing to as much as 1200 lpm. Line printers print a complete line at a time and have speeds in the range of 150 to 2500 lines per minute.
  The types of line printers are drum printers, band-printers, and chain printers. Other non-impact technologies have also been used, as thermal line printers were popular in the 1970s and 1980s, and some inkjet and laser printers produce output a line or a page at a time.
context_section_description: In a typical drum printer design, a fixed font character set is engraved onto the periphery of a number of print wheels, the number matching the number of columns (letters in a line) the printer can print.  The wheels, joined to form a large drum (cylinder), spin at high speed and paper and an inked ribbon is stepped (moved) past the print position.  As the desired character for each column passes the print position, a hammer strikes the paper from the rear and presses the paper against the ribbon and the drum, causing the desired character to be recorded on the continuous paper. Because the drum carrying the letterforms (characters) remains in constant motion, the strike-and-retreat action of the hammers has to be very fast. Typically, they are driven by voice coils mounted on the moving part of the hammer.
  Often the character sequences are staggered around the drum, shifting with each column. This prevents firing all of the hammers simultaneously when printing a line that consists of the same character in all columns, such as a complete line of dashes ("--------...") (but allows it when the printed line matches the character layout on the drum ("@ABCDEFGHIJKLMNOP@ABCDEFGHIJKLMNOP...")).
  Lower-cost printers do not use a hammer for each column. Instead, a hammer is provided for every other column and the entire hammer bank is arranged to shift left and right, driven by an additional voice coil. For this style of printer, two complete revolutions of the character drum ara required with one revolution being used to print all the "odd" columns and another revolution being used to print all of the "even" columns; however, on the plus side, only half (plus one) the number of hammers, magnets, and the associated channels of drive electronics are required.
  At least one low-cost printer, made by CDC, achieves the same end by moving the paper laterally while keeping the hammer bank at rest.
  Dataproducts was a typical vendor of drum printers, often selling similar models with both a full set of hammers (and delivering, for example 600 lines-per-minute of output) and a half set of hammers (delivering 300 LPM).
caption: Fragment of line printer drum
  showing "%" characters.
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