The Digital Equipment Corporation PDP–7

PDP-7 sales photo
PDP–7 sales photo
A PDP-7/A in manufacture
A PDP–7/A in manufacture
(Concord Control Corporation)
PDP-7/A S#115 undergoing restoration in Oslo Norway, by Tore Sinding Bekkedal
PDP–7/A S#115 undergoing
restoration in Oslo Norway
©2009 Tore Sinding Bekkedal

1964–65 saw the delivery of the third design in Digital Equipment Corporation's series of 18–bit computers[1] - the PDP–7, the first of their computers to use "FlipChip" technology.  A later PDP–7 revision, the PDP–7/A, was produced using R series modules, and at the end of production a total of 99[2] PDP–7 and PDP–7/A systems had apparently been shipped.  As a minicomputer the PDP–7 had a cycle time of 1.75 microseconds[3] and an add time of 4 microseconds, I/O included a keyboard, printer, paper–tape and dual transport DECtape drives (type 555).  Of the original sales target of 120 PDP–7 systems, quite a number were used in laboratory and data acquisition applications and it remained in production for five years.  DEC provided an "advanced" Fortran II compiler, a Symbolic Assembler, Editor, DDT Debugging System, Maintenance routines and a library of arithmetic, utility and programming aids developed on the program–compatible PDP–4.

The PDP–7 was developed as a less expensive alternative to the earlier PDP range and it had an introductory price tag of only $72,000 for a minimal system configuration (options list).  Utilising core memory as did most machines of its era, the PDP–7's 18–bit memory started at 4K words, upgradeable in 4K chunks to a maximum of 64K, a miniscule amount by today's standards!  There was range of I/O units available including Calcomp plotters, DECtape magnetic tape, paper tape readers and high speed paper tape punches, a DEC 340 CRT display unit and the ubiquitous Teletype ASR33.

The PDP–7's claim to fame was forged around 1969–70 when Ken Thompson used a scavenged PDP–7 at Bell Labs, the research arm of AT&T, to develop the operating system that later became Unix.  (From the 18–bit Service list this would appear to have been one of PDP–7's #3, #34, #44 or PDP–7/A S#149.

PDP is an abbreviation for Programmed Data Processor, coined by Digital Equipment Corporation and a Boston venture capital company American Research and Development.  There was a perceived view at the time that with a limited world market for "Computers" of just a few hundred, of what were seemingly big and expensive machines requiring a dedicated computer centre and a large supporting staff, the term "Computer" should be avoided as there was no money to be made in computers! (doh!), and so was born the PDP - the "Programmed Data Processor".

December 2019 -   Of the supposedly 120 PDP–7's originally built (99 traceable) only four had been confirmed to exist in the wild, with only one being in an operable condition.  However as of November 2019 several sources have contacted us to let us know of a 5th machine that has been recently donated to, and installed at, The Living Computer Museum (Seattle, Washington) and that it is now running Unix V0.  Originally delivered to Boeing it is believed that the Boeing Development Center’s PDP–7 was interconnected with an SDS 940, forming a system to display processed data.  There is only one PDP–7 listed at Boeing in the DEC PDP–7 service list, that being machine #129, a PDP–7A, delivered in August 1966 and listed as "Boeing Co. #2", the list does not appear to have a "Boeing #1".  See link #5 below.

  1. S#47, is a minimal configuration system at a museum in Australia owned by Max Burnet, who has kindly provided photos and information about the system and DEC Australia in general.  The Computer History Museum (Mountain View, California), also have several photos of PDP–7 systems in manufacture including two views of #47 that was shipped to the Australian Atomic Energy Commission.
  2. S#113, at the University of Oregon was operated by Dr. Harlan Lefevre until his retirement when it was decommissioned and donated to the Paul G. Allen PDPplanet collection.  It is believed this machine was still fully operational after nearly 40 years with some 65,000 hours (or 7½ years continuous) of use logged[4].  It was due to be recommissioned in 2009, however this was eventually completed during 2010, see the Living Computer Museum website.
  3. S#115, is apparently undergoing restoration in Oslo, Norway by Tore Sinding Bekkedal, but it is believed that as this machine had most of its guts modified to TTL 74 series logic at some point in its life, which was then recovered when the machine was decommissioned, bringing it back to full operation was not possible.
  4. S#33.  Rumours of a fourth PDP–7 system at the Computer History Museum have now been confirmed as true following an email from Len Shustek, chairman of the museum.  The museums online entry for this machine is online.  This machine is listed as being from Massachusetts General Hospital so would have been either PDP–7 S#33 or PDP–7/A S#103, from the photos we suspect it is #33.
  5. S#129.  The Living Computers museums blogs -
    Restoring UNIX v0 on a PDP–7: A look behind the scenes - November 1, 2019
    Unix Version 0 on the PDP–7 at LCM+L - November 13, 2019

Ken Olsen, co-founder of Digital Equipment Corporation

6th February 2011 - Ken Olsen.

We have received the sad news that Ken Olsen co–founder of Digital Equipment Corporation, has died at the age of 84.  Digital Equipment Corporation during the 1960's through to the 1980's was one of the major players in the computer industry with their range of PDP and VAX series computers.  Ken died on Sunday, February 6, 2011.  He would have been 85 years old on February 20.  Our condolences to Ken's family.  (Obituary, copy).

Links -

Tore Bekkedal, as of July 2020 this site is offline.Restoration of a PDP–7 in Oslo.
PDP–7 dataPossibly the largest archive of PDP–7 data available.
Unix historyOrigins and History of Unix (Wikipedia).
HistoryUnix - "The famous PDP–7 comes to the rescue".
WikipediaPDP–7 entry at Wikipedia.
PDP–7 Service listDetails of the known 99 PDP–7 systems built (1972).

If you know of any more information about the PDP–7, options, location of existing systems, spare parts, ancillary bits, software, tapes or manuals, then please let us know.

Further reading on PDP–7 history and design.

Our own library of PDP–7 information.

PDP–7 Service list (1972)
The following list information was compiled from Digital Equipment Corporation's 1972 18–bit Customer Service List (kindly supplied by Bob Supnik), available as a download (6.5Mb pdf), and lists the 99 known PDP–7 and PDP–7/A systems on the list in 1972.  120 systems were forecast to be built in total, but at this time we do not have any further information about the possible remaining 21 systems or if they were even built.  The PDP–7 appeared to have sold well into Government research and University sectors with 11 systems shipped to the UK alone, almost 10% of the forecast production run!  Serial numbers are concurrent for both PDP–7's and the PDP–7/A's giving 102 systems shipped but with three missing in the list.  The missing 21 could be of either type; however we are now confident that the 99 systems shipped were the only ones ever built.

Systems in green are systems existing today in museums or private collections, although not necessarily in an operational state.  Two machines however, S#113 and S#129, have been restored and are now fully operational and open to public viewing at the Living Computer Museum in Seattle.  The 18–bit Customer Service List covers PDP–7 S#1–50 with S#22 and S#46 missing and PDP–7/A's S#101–152 with S#125 missing, making it 99 systems shipped of the potential 102 serial numbers.

1-DEC prototype
204/1965Stanford University (Palo Alto, California USA) - info
311/00 ?Bell Telephone Labs (USA)
401/1965R Boisurt (?)
504/00 ?New York University (USA)
604/1965TH Delft (University of Delft, The Netherlands)
702/1965Elliot Cambridge (UK)
804/1965Holloman A.F.B. (New Mexico USA)
905/1965Rensselaer Polytechnic (Troy, New york USA)
1004/00 ?Fort Belvoir (Fairfax County, Virginia USA)
1110/00 ?Oxford University (UK)
1205/1965Tekniska Högskolan (Helsinki University of Technology, Sweden)
1305/1965Pittsburgh University (which one? Pennsylvania USA)
1404/1965Foxboro Pureto (Puerto) Rico
1505/1965Jet Propulsion Laboratory (Pasadena, California USA)
1605/1965Argonne National Labs (Argonne, Illinois USA)
1708/1965University of Texas (Austin, Texas USA)
1805/1965Carnegie Tech (Carnegie Mellon University? Pittsburgh, Pennsylvania USA)
1905/1965Massachusetts Institute of Technology Lincoln Labs (Lexington, Massachusetts USA)
2005/1965Battelle Northwest (Pacific Northwest National Laboratory, Richland, Washington USA)
2105/1965Battelle Northwest (Pacific Northwest National Laboratory, Richland, Washington USA)
22?No information available
2307/1965Jet Propulsion Laboratory (Pasadena, California USA)
2408/00?Massachusetts Institute of Technology #2 (Lincoln Labs? Lexington, Massachusetts USA)
2508/1968Manchester University (UK)
2608/1965Alabama University (Tuscaloosa, Alabama USA)
2707/1965Stromberg Carlson (Telecommunications? Rochester New York USA)
2807/1965WPAFB / AZERP #1 (Wright–Patterson Air Force Base? Ohio USA)
2912/1965Foxboro (Puerto Rico? S#14)
3009/1965Massachusetts Institute of Technology Lincoln Lab MONT (Lexington, Massachusetts USA)
3109/1965LRL Berkeley (Lawrence Radiation Laboratory, Berkeley, California USA)
3209/1965Lear Siegler (California? USA)
3307/1965Massachusetts General Hospital #1 (Boston USA) - info
Either this machine or S#103 is now at the Computer History Museum collection in Mountain View, California - CHM website
3401/1969Bell Telephone Labs (USA)
Recent research by Warner Losh in his blogs #1 and #2 have shown that this PDP–7 at Bell Telephone Labs is the one that Ken Thompson and Dennis Ritchie "scrounged" and then used to develop UNIX.
3510/1965University of Illinois (Champaign? Illinois USA)
3610/1965Jet Propulsion Laboratory (California Institute of Technology? Pasadena, California)
3712/1967US Naval Ordinance
3808/1968US Government
3912/00?Tennessee University (Knoxville Tennessee USA)
4012/1965Module test
4111/1965Ministry of Public Buildings (UK Government N.G.T.E Pyestock) - info - website
4211/1965Aachen #1 (Aachen Technical School? Aachen, Germany)
4311/1965LRL Livermore (Lawrence Radiation Laboratory, Livermore? California USA)
4411/1965Bell Telephone Labs (USA)
4512/1965Hershey Medical Centre (Hershey, Pennsylvania USA)
46?No information available
4701/1966Australian Atomic Energy, Lucas Heights - info
This machine is now in the private collection of Max Burnet in Australia
4801/1966Jet Propulsion Laboratory
4901/00 ?University of Heledelberg FSIC (Heidelberg Germany?)

10112/1969Bob Reed
10208/1968University of Rochester (Rochester USA)
10301/1966Massachusetts General Hospital #2. (Boston USA) - info
Either this machine or S#33 is now at the Computer History Museum collection in Mountain View, California - CHM website
10401/1966Massachusetts Institute of Technology, project MAC - info
10501/1966University of Freiburg (Freiburg, Germany)
10601/00 ?Liverpool University (UK)
10701/00 ?Glasgow University (UK)
10801/00 ?Aachen #2 (Aachen Technical School? Aachen, Germany)
10901/1970Massachusetts Institute of Technology ERC (Education Research Centre), Cambridge, Massachusetts USA - info
11102/1966Atomic Weapons Research Establishment (A.W.R.E.) Aldersmaston (UK)
11202/1966Edinburgh University (UK) - info
11302/1966Oregon University - info
This machine is now in the Paul G. Allen PDPplanet collection at the Living Computer Museum, Seattle. It completed restoration during 2010 LCM website
11402/1966Applied Data Research
11502/1966Oslo University, Norway - info
This machine is now in the private collection of Tore Sinding Bekkedal in Oslo.  It was apparently undergoing restoration but this is believed to have now stopped. (website currently offline)
11604/1966TNO Soesterberg (The Netherlands)
11703/00 ?Tokyo University Japan
11804/1966Worcester Polytechnic (Massachusetts USA)
11905/1966DEC training (UK)
12006/1966Michigan University (Michigan USA) - info
12105/1966Fort Meade #1 (Baltimore USA)
12211/1966Fort Meade #2 (Baltimore USA)
12303/00 ?US Government Virginia
12404/1966University of Nijmegen (The Netherlands)
125?No information available
12605/1966University of Cambridge (UK) - info   info
12706/1966Information Intern
12803/1969University of Erlangen (Nuremberg, Germany)
12908/1966Boeing Co. #2
This machine was recently donated to the Paul G. Allen PDPplanet collection, Seattle.  In late 2019 it was used to boot and run UNIX V0. LCM Website
13008/1966University California LRL (Lawrence Radiation Laboratory? Berkeley California USA)
13106/1966University of Pittsburgh (Pittsburgh Pennsylvania, United States)
13206/1966DEC training (UK)
13310/1966Imperial College (London UK)
13403/1968Rome Air Force Base (Italy? or Griffiss Air Force Base? Rome New York USA)
13510/00?Princeton University (New Jersey USA)
13611/1966Fort Meade US Army #3 (Baltimore USA)
13708/1966Union Carbide (? USA)
13810/1966Timesharing Ltd. (TimeSharing Ltd London UK)
13911/1966Yale (New Haven, Connecticut USA)
14011/00 ?Sandia Corp. (California or New Mexico? USA) - photos 1, 2
14109/00 ?WPAFB #2 (Wright–Patterson Air Force Base? Ohio USA))
14212/00 ?PGH Plate Glass Co. (Pittsburgh? USA)
14303/1969Four Queens Casino O? LAS (Las Vegas? Nevada USA)
14401/1970University of California (New York? USA)
14512/00 ?Langley Porter (UCSF Medical Centre? San Francisco, California USA)
14611/00 ?University of Paris (Paris, France)
14707/1967III (Information International Inc. also Triple-I)
14801/1967BBN (Bolt, Beranek and Newman, Boston Massachusetts USA)
14903/1969Bell Telephone Labs (USA)
15001/1967BBN (Bolt, Beranek and Newman, Boston Massachusetts USA)
15109/00 ?Digital Circuit Tester
15204/00 ?Royal Radar Establishment Malvern (UK)

A full list, to our knowledge, of the available options on a PDP–7 is available.

Miscellaneous DEC information, manuals, data sheets, Etc. mostly for the PDP–7 of course! but there is some PDP–11 and PDP–15 info in here as well.

Brochure 1964
1.1Mb pdf
Brochure F–71 from 1964 entitled - "Programmed Data Processor - 7", a basic brochure of the PDP–7.
Brochure 1964
4.8Mb pdf
A more involved DEC brochure from 1964 giving a good basic run down of the PDP–7 computer, its basic operation and options.
Logic handbook 1961
5Mb pdf
DEC symbology, Basic digital modules (inverters; diode logic; flip–flops; delays; pulse amplifiers; clocks; pulse generators), Typical applications (counters; parallel adders; comparators; synchronizers; subtracters; Gray to binary code converter), Rules and definitions (inverter usage; loading definitions; marginal checking; indicators), Boolean algebra, DEC Technical bulletins.
Logic handbook 1967
26Mb pdf
Logic primer, R B W Series "FlipChip" modules and application notes (32 position decoding; Stepper motor drives; Pseudo random sequences), Logic laboratory, Hardware (panels; cabinets; hardware; connectors; Octaid and Panelaid series modules; E and F Series modules), Analog to Digital Conversion handbook, A Series modules, K Series modules, and a whole lot more!
Technicians handbook 1974
3.6Mb pdf
1974 Technicians handbook from the DEC training department in Galway Ireland.  Includes PDP8, PDP11 and IC information.  Trouble shooting, General notes, PDP8 family notes, PDP11 family notes, IC datasheet index (DEC numbers; 74xx 8xxx and 9xxx series IC's).
Users Handbook 1965
13.5Mb pdf
System introduction, Functional description, Instructions, Basic machine language programming, Processor, Core memory, Standard I/O equipment, Card equipment and line printer, Magnetic tape and drum, Plotter and display, Analog/digital conversion, Data and communication equipment, Operating procedures, Fortran, appendix, illustrations.
Users Handbook 1964
7.4Mb pdf
Description, Operation, Central processor, Input/output control and interface, Input/output equipment, Appendix, Illustrations and drawings.
Maintenance Manual 1966
20Mb pdf
For PDP–7/A systems (serial numbers 100 and above).  Introduction and description, Operation, System, options, Maintenance, Engineering drawings, Power supplies and control, FlipChip modules.
18–bit Architecture
113Kb pdf
Architectural Evolution in DEC's 18–bit Computers.  DEC built five 18–bit computer systems: the PDP–1, PDP–4, PDP–7, PDP–9, and PDP–15.  This paper documents the architectural changes that occurred over the lifetime of the 18–bit systems and analyses the benefits and trade–offs of the changes made.  Written and ©2006 Bob Supnik. (2003 original 90Kb pdf)
18–bit Card readers
34Kb pdf
Card Readers for DEC's 18–bit Computers.  Punched cards were never a mainstream medium for DEC systems.  DEC preferred punched paper–tape, which used less costly peripherals and simpler interfaces.  DEC never seemed to be able to get cards quite right.  Nowhere is this better illustrated than in the 18–bit computer line, which implemented seven different card reader options across the five machines in the 18–bit family PDP–1, PDP–4, PDP–7, PDP–9, and PDP–15.
Interface manual
4.9Mb pdf
PDP–7 Interface and installation manual.  Introduction, Data transfers, Break transfers, Digital logic circuits, Interface connections, Installation planning, Illustrations, Tables.  Information in this manual applies only to PDP–7 systems with serial numbers above 100.  Refer to the PDP–7 Interface and Installation Manual, F–78, dated 1/66, for information on systems with serial numbers below 100.
Maintenance manual
23.5Mb pdf
Core memory, Input/output, Optional equipment, Interface, Installation, Operation, Maintenance, Engineering drawings, Tables.
PDP–7/A S#113
10.0Mb pdf
PowerPoint presentation made by Professor Lefevre of The University of Oregon about the history and restoration of their PDP–7/A, now at the Living Computer Museum.
PDP–7 - DEC–388
Display interface
2.3Mb pdf
Dated August 1967, this document (Report #?) contains a description, commands and hardware drawings of a PDP–7 modified for use with a DEC 388 display usually used on a PDP–8.  Known locally as the 337 it became the prototype for the DEC 339 display.  The document is in the public domain, copyright of this document resides with the University of Michigan, Ann Arbor.
Software manual
6.1Mb pdf
Dated November 1968, this document (Report #10) describes LOCOSS, Logic Of Computer Operating System for the PDP–Seven, developed to provide a run–time environment for application programs.  The document is in the public domain, copyright of this document resides with the University of Michigan, Ann Arbor.
PDP–7 - IBM 1800
Interface software
4.5Mb pdf
Dated December 1968, this document (Report #11) contains a description of a collection of programs for the PDP–7 to IBM 1800 inter–computer data link including file manipulation, text editors, assemblers and debugging.  The document is in the public domain, copyright of this document resides with the University of Michigan, Ann Arbor.
PDP–7 - IBM 1800
1.5Mb pdf
Dated November 1968, this document (Report #12) contains a functional description of the high speed interface.  The document is in the public domain, copyright of this document resides with the University of Michigan, Ann Arbor.
PDP–7 - IBM 1800
Interface manual
8.6Mb pdf
Dated August 1970, this document (Report #31) contains a description, commands and hardware drawings of a PDP–7 to IBM 1800 inter–computer data link, with basic diagrams.  Again, it is not known if this interface existed but the general tone of the report suggests it did.  The document is in the public domain, copyright of this document resides with the University of Michigan, Ann Arbor.
The University of Michigan had a PDP–7/A S#120, delivered in 1966.
PDP–7 - PDP–9
Comms package
2Mb pdf
Dated July 1970, this document contains a description and commands of a PDP–7 to PDP–9 inter–computer data link using a 50 kilobit serial Dataphone link.  The document (memorandum 11) is in the public domain, copyright of this document resides with the Massachusetts Institute of Technology.
M.I.T.  had a PDP–7/A S#104, delivered to project MAC (Technology Square) in 1966.

  1. DEC 18–bit Computers – [top]

    1. PDP–1 - 4K–64K of main memory, 5uS cycle time, one's complement arithmetic.  Mostly constructed of DEC 1000–series system building blocks rated at 5MHz.  Apparently three PDP–1 computers still exist, all in the collection of the Computer History Museum, a prototype, and two PDP–1C machines.  The last PDP–1 manufactured (#55) has been restored to working order and is used as a working exhibit.
    2. PDP–4 - First shipped in July 1962 as a slower, cheaper alternative to the PDP–1, but not commercially successful.  One customer of these early PDP machines was Atomic Energy of Canada.  The PDP–4 has been implemented by David Conroy in a XILINX field programmable gate array.
    3. PDP–7 - Replacement for the PDP–4, DEC's first wire–wrapped machine.
    4. PDP–9 - Successor to the PDP–7, DEC's first micro–programmed machine.
    5. PDP–15 - DEC's final 18–bit machine.  It was their only 18–bit machine constructed from TTL integrated circuits rather than discrete transistors.  Later versions of the system were referred to as the "XVM" family.  The new machine was faster and less expensive than its predecessors and had the added sophistication of a separate I/O processor to the CPU.  Over 400 of these machines were ordered in the first eight months of production.  PDP–15's in the collection of Mike Ross

  2. Various information sources on both the internet and in literature gives the total sales of the PDP–7 systems as 120 units, in our research however we have not found any definitive information to substantiate this number.  To date the only firm evidence for the number of systems produced is the 1972 18–bit Service list, which shows 99 systems.  Unless further information surfaces in the future, which is now probably unlikely, 99 shipped systems it will have to be. [top]

    1. From the DEC book "Computer Engineering - A DEC view of hardware systems design", it is apparent that the original - sales goal – for the PDP–7 range was 120 units.
    2. The 1978 DEC historical document "Nineteen Fifty–Seven To The Present" copy here, has (on page 6) that "One hundred and twenty PDP–7's were sold altogether", whilst on page 86 in the table of "Installed minicomputer Systems", it lists the PDP–7 as having 115 installed systems at January 1st 1977 with deliveries starting in November 1964.  It cites the International Data Corporation EDP Industry Report 22nd April 1977.c

  3. A find in DECuscope Volume 10 1971, the newsletter of the Digital Equipment Users Society, has unearthed an article by A. R. Atherton of the Cavendish Laboratory, Cambridge, England (PDP–7/A S#126), entitled "MODERNIZING A PDP–7", where a new 16K core store was fitted to their PDP–7 and the opportunity taken to reduce the cycle time of the computer from 1750nsec to 875nsec, doubling its speed.  A supercharged PDP–7!! [top]

  4. Longevity - DEC PDP–7's were all fitted with a running hour meter recording the number of hours spent in operation.  We currently have the values for two PDP–7 systems when they were finally de–commissioned - [top]

    1. #113, at the University of Oregon - 65,000 hours of use (or 7½ years continuous) logged after nearly 40 years.  Delivered in February 1966 and scheduled for removal at the end of 2001, #113 would appear to have lingered on at the University for another five years until finally being moved in June 2006 when it was still in a running condition.  This machine is now at Paul Allen's Living Computer Museum (PDPplanet Project) in Seattle.  It has been restored and is now fully operational and open to public viewing at the museum.
    2. #47, at the Australian Atomic Energy Commission Lucas Heights - 111,577 hours of operation (or 12¾ years continuous). Delivered in 1966 and retired after 15 years to the museum of Digital Equipment Australia PTY Ltd. run by Max Burnet, the company's general manager.  This machine was switched on for over 12.5 years of its 15 year lifetime at Lucas Heights.

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