The PDP-4 was the successor to the Digital Equipment Corporation's PDP-1.

Photograph of Exhibit of PDP-4 Digital Equipment Corporation Machines on the Stage of the National Archives Auditorium, 1964 (3874706978).jpg
PDP-4 computer
DeveloperDigital Equipment Corporation
Product familyProgrammed Data Processor
Release date1962; 59 years ago (1962)
Introductory priceUS$65,000
Units soldApproximately 54
MediaPaper tape
PlatformDEC 18-bit
Mass1,090 pounds (490 kg)


This 18-bit machine, first shipped in 1962,[1] was a compromise: "with slower memory and different packaging" than the PDP-1, but priced at $65,000 - less than half the price of its predecessor.[2]: p.4  All later 18-bit PDP machines (7, 9 and 15) are based on a similar, but enlarged instruction set, more powerful than, but based on the same concepts as, the 12-bit PDP-5/PDP-8 series.

Approximately 54 were sold.[2]


The PDP-4's console typewriter was a Teletype Model 28 ASR, with a built in paper tape reader and paper tape punch.

The system's memory cycle was 8 microseconds, compared to 5 microseconds for the PDP-1.[3][4]

The PDP-4 weighed about 1,090 pounds (490 kg).[5]

Mass storageEdit

Both the PDP-1 and the PDP-4 were introduced as paper tape-based systems.[6] The only use, if any, for IBM-compatible 200 BPI or 556 BPI magnetic tape[7] was for data. The use of "mass storage" drums - not even a megabyte and non-removable - were an available option, but were not in the spirit of the “personal” or serially shared systems that DEC offered.

It was in this setting that DEC introduced DECtape, initially called "MicroTape", for both the PDP-1 and PDP-4.


DEC provided an editor, an assembler, and a FORTRAN II compiler.[3] The assembler was different from that of the PDP-1 in two ways:

  • Unlike the PDP-1, macros were not supported.
  • It was a 1-pass assembler; paper-tape input did not have to be read twice.


See alsoEdit


  1. ^ Robert Slater (1989). Portraits in Silicon. p. 210. ISBN 0262691310.
  2. ^ a b DIGITAL EQUIPMENT CORPORATION - Nineteen Fifty-Seven To The Present (PDF). Digital Equipment Corporation. 1975.
  3. ^ a b Paul E. Ceruzzi (2012). A History of Modern Computing. p. 209. ISBN 0262532034.
  4. ^ Bell, C. Gordon; Mudge, J. Craig; McNamara, John E. (2014). Computer Engineering: A DEC View of Hardware Systems Design. ISBN 1483221105.
  5. ^ Weik, Martin H. (Jan 1964). "PROGRAMMED DATA PROCESSOR 4". A Fourth Survey of Domestic Electronic Digital Computing Systems.
  6. ^ Bob Supnik. "Architectural Evolution in DEC's 18b Computers" (PDF).
  7. ^ Brochure F-71 - "Programmed Data Processor - 7" (PDF). Digital Equipment Corporation. 1964.