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DECtape

A TU56 dual DECtape unit for a DEC PDP-11. Note the 6-armed "starfish" hubs holding circular white tape reels in place. The vertical aluminium block above each pair of tape reels holds the read/write heads.

DECtape, originally called Microtape, is a magnetic tape data storage medium used with many Digital Equipment Corporation computers, including the PDP-6, PDP-8, LINC-8, PDP-9, PDP-10, PDP-11, PDP-12, and the PDP-15. On DEC's 32-bit systems, VAX/VMS support for it was implemented but did not become an official part of the product lineup.

DECtapes[1] are 3⁄4 inch (19 mm) wide, and formatted into blocks of data that can each be read or written individually. Each tape stores 184K 12-bit PDP-8 words or 144K 18-bit words. Block size is 128 12-bit words (for the 12-bit machines), or 256 18-bit words for the other machines (16, 18, 32, or 36-bit systems).[2]

From a programming point of view,[1]: p.505 [3] because the system is block-oriented and allows random seeking, DECtape behaves like a very slow disk drive.[4]

  1. ^ a b Bell, C. Gordon; Mudge, J. Craig; McNamara, John E. (1978). COMPUTER ENGINEERING: A DEC View of Hardware Systems Design. Bedford, Mass.: Digital Press. ISBN 9781483207674.
  2. ^ David Donald Miller (1997). Open VMS Operating System Concepts. p. 440. ISBN 978-1555581572.
  3. ^ A file system was developed for it, and is included in the PDP-6 monitor.
  4. ^ A PDP-6 using only DECtape, that formerly supported 4-6 timesharing users could, with a single disk drive, support up to 30 users - p.35, Volume 1, Number 1, The DEC Professional (magazine)

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