PDP-5

The PDP-5 was Digital Equipment Corporation's first 12-bit computer, introduced in 1963.[2]: p.5 

PDP-5
DeveloperDigital Equipment Corporation
Product familyProgrammed Data Processor
TypeMinicomputer
Release date1963 (1963)
Introductory priceUS$27,000
Units soldabout 1,000[1]
PlatformDEC 12-bit
Mass540 pounds (240 kg)
PredecessorLINC
SuccessorPDP-8

History

An earlier 12-bit computer, named LINC has been described as the first minicomputer[3] and also "the first modern personal computer."[4] 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.

Applicability

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"[5]
  • "Very reliable data was obtained with ..."[6]
  • "A PDP-5 computer was used very successfully aboard Evergreen[NB 1] for ..."[7]

all of which described the same PDP-5 used by the United States Coast Guard.

The architecture of the PDP-5 was specified by Alan Kotok and Gordon Bell; the principal logic designer was the young engineer Edson de Castro[8][9] who went on later to found Data General.

Hardware

By contrast with the 4-cabinet PDP-1,[10] the minimum configuration of the PDP-5 was a single 19-inch cabinet with "150 printed circuit board modules holding over 900 transistors."[11] Additional cabinets were required to house many peripheral devices.

The minimum configuration weighed about 540 pounds (240 kg).[12]

The machine was offered with from 1,024 to 32,768 12-bit words of core memory. Addressing more than 4,096 words of memory required the addition of a Type 154 Memory Extension Control unit (in modern terms, a memory management unit); this allowed adding additional Type 155 4,096 word core memory modules.[13][14]

Instruction set

Of the 12 bits in each word, exactly 3 were used for instruction op-codes.[13][15]

The PDP-5's instruction set was later expanded in its successor, the PDP-8. The biggest change was that, in the PDP-5, the program counter was stored in memory location zero, while on PDP-8 computers, it was a register inside the CPU. Another significant change was that microcoded instructions on the PDP-5 could not combine incrementing and clearing the accumulator, while these could be combined on the PDP-8. This allowed loading of many small constants in a single instruction on the PDP-8. The PDP-5 was one of the first computer series with more than 1,000 built.[16][1]

Software

DEC provided an editor, an assembler, a FORTRAN II Compiler and DDT (a debugger).[13]

Marketplace

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.[17][2]

Photos

Notes
  1. U. S. Coast Guard Oceanographic Vessel — Evergreen (WAGO-295)

References
  1. "PDP-5 Historical Interlude". 11 December 2014.
  2. DIGITAL EQUIPMENT CORPORATION – Nineteen Fifty-Seven To The Present (PDF). Digital Equipment Corporation. 1975.
  3. "Wesley Clark Builds the LINC, Perhaps the First Mini-Computer".
  4. John Markoff, New York Times (March 4, 2016). "Wesley A. Clark, 88; MIT pioneer made computing personal". The Boston Globe (NY Times-owned).
  5. 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. "COAST GUARD WASHINGTON D C OCEANOGRAPHIC UNIT". WorldCat.org.
  7. Herbert W. Graham (3 May 2022). "United States Report to ICNAF On Status of the Fisheries and Research Conducted in Calendar Year 1965" (PDF). p. 1a.
  8. Best, Richard; Doane, Russell; McNamara, John (1978). "Digital Modules, The Basis for Computers". Computer Engineering, A DEC view of hardware systems design (PDF). Digital Press. Archived (PDF) from the original on 2010-03-12.
  9. Reddy, Raj. "Nomination form for Edson de Castro to the National Academy of Engineering". Carnegie Mellon University Libraries Digital Collections. Carnegie Mellon University. Archived from the original on 2018-01-22.
  10. Ed Thelen. "PDP-1".
  11. "The Rise and Fall of Minicomputers". 24 October 2019.
  12. PDP-5 Maintenance Manual (PDF). Digital Equipment Corporation. October 1964. p. 1-13.
  13. Programmed Data Processor 5, Digital Equipment Corp., Mar. 1964; this is a promotional brochure.
  14. "PDP-5 Price List" (PDF). Digital Equipment Corporation. October 1969.
  15. Programmed Data Processor-5 Handbook (PDF). Digital Equipment Corporation. 1964. p. 12.
  16. "Programmed Data Processor-5".
  17. "Who Built the First Minicomputers Part II".
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