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The PDP-5 was Digital Equipment Corporation's first 12-bit computer, introduced in 1963.[1]:p.5

d-i-g-i-t-a-l (Logo)


An earlier 12-bit computer, named LINC has been described as the first minicomputer[2] and also "the first modern personal computer."[3] It had 2,048 12-bit words, and the first LINC was built in 1962.

DEC's founder, Ken Olsen, had worked with both it and a still earlier computer, the 18-bit 64,000-word TX-0, at MIT's Lincoln Laboratory.

Neither of these machines was mass-produced.


Although the LINC computer was intended primarily for laboratory use, the PDP-5's 12-bit system had a far wider range of use. An example of DEC's "The success of the PDP-5 ... proved that a market for minicomputers did exist" is:

  • "Data-processing computers have accomplished for mathematicians what the wheel did for transportation"[4]
  • "Very reliable data was obtained with ..."[5]
  • "A PDP-5 computer was used very successfully aboard Evergreen[NB 1] for ..."[6]
all of which described the same PDP-5 used by the Coast Guard.

The principal designer of the PDP-5 was the young engineer Edson de Castro[7] who went on later to found Data General.


By contrast with the 4-cabinet PDP-1,[8] the PDP-5 was a single 19-inch cabinet with "150 printed circuit board modules holding over 900 transistors."[9]

The PDP-5 weighed about 540 pounds (240 kg).[10]

A maximum of 4,096 12-bit words could be addressed.

Instruction set[edit]

Of the 12 bits in each word, exactly 3 were used for instruction op-codes.[11][12]

The PDP-5's instruction set was later expanded in its successor, the PDP-8, such that bit rotations could be combined with IAC and CLA to effectively load small constants in a single instruction. The PDP-5 was the first computer series with more than 1,000 built,[13][14] which was a large number in the decade after ENIAC/UNIVAC builders predicted that 3 computers would serve the nation's computing needs.


DEC provided an editor, an assembler, a FORTRAN II Compiler and a debugging tool.[15]


With a base price of $27,000 and designed for those not in need of the 18-bit PDP-4, yet having "applications needing solutions too complicated to be solved efficiently by modules systems" the PDP-5, when introduced in 1963, came at a time when the minicomputer market was gaining a foothold.[16][1]



  1. ^ U. S. Coast Guard Oceanographic Vessel Evergreen


  1. ^ a b DIGITAL EQUIPMENT CORPORATION - Nineteen Fifty-Seven To The Present (PDF). Digital Equipment Corporation. 1975.
  2. ^ "Wesley Clark Builds the LINC, Perhaps the First Mini-Computer".
  3. ^ John Markoff, New York Times (March 4, 2016). "Wesley A. Clark, 88; MIT pioneer made computing personal". The Boston Globe (NY Times-owned).
  4. ^ John P. Callahan (June 14, 1965). "COMPUTER AN AID IN OCEAN STUDIES; Statistical Tasks Are Eased During Ice Patrol Season 1964". The New York Times.
  6. ^ Herbert W. Graham. "United States Report to ICNAF On Status of the Fisheries and Research Conducted in Calendar Year 1965" (PDF). p. 1a.
  7. ^ Reddy, Raj. "Moza Bint Nasser University Professor of Computer Science and Robotics in the School of Computer Science at Carnegie Mellon University". Carnegie Mellon University Libraries Digital Collections. Carnegie Mellon University. Retrieved 22 January 2018.
  8. ^ Ed Helen. "PDP-1".
  9. ^ "The Rise and Fall of Minicomputers".
  10. ^ "PDP-5 documents". www.bitsavers.org. F-57_pdp5maint_Oct64.pdf, p. 1-13 (29).
  11. ^ Ed Thelen. "PDP-5".
  12. ^ "Programmed Data Processor-5 Handbook" (PDF). Digital Equipment Corporation. 1964. p. 12.
  13. ^ "Programmed Data Process-5".
  14. ^ "PDP-5 Historical Interlude".
  15. ^ "DEC.PDP-5.1964".
  16. ^ "who built the first minicomputer".