This website is a 'scratchpad' for my PDP-1 and PiDP-1 Computer System documentation. This is not a reference site and it is highly likely anybody landing on this Home Page will be better served by referring to one of the following:-
As at October 1st, 2026, the book PiDP-1, A Programmed Data Processor, by Andrew Barron has the most comprehensive collection of PiDP-1 material. This book takes the PiPD-1 from an introduction through construction to the upgrades and expansion provided by Bill Ezell's software on Github. It should be obvious that I've failed to recommend this site.
In the construction. installation, programming, operation and maintenance of a PiDP-1 system the open nature of this project will include variations and different interpretations. I'm including my comments a PiDP-1 Notes section.
This document is mostly a collection of incomplete and broken references. Just so incomplete that it is of doubtful utility to anybody at this stage, myself included. This document also includes my guesstimates that may or may not have some vague connection to reality,
This site is just going to use RAW HTML5 without CSS, etc., so don't wait for the pretty version. At the present time I have not included the
You have been warned! I'll show some restraint by only using one Exclamation Mark.
The PDP-1 (Programmed Data Processor) was the first computer system released by Digital Equipment Corporation (DEC). The PDP-1 was announced December 1, 1959 at the Eastern Joint Computer Conference in Boston and production was discontinued in 1969. Refer to the Wikipedia PDP-1 entry for an overview.
A major hurdle is the PDP-1 predates the Intertubes and information has been lost. A significant percentage of the information that was preserved is not available online. When looking at DEC's PDP-1 documentation and code fragments I kept running across mnemonics that were missing from DEC's PDP-1 Handbook. My starting point was to assemble the available information for all PDP-1 systems.
Wikipedia as at September 17, 2026 states 53 PDP-1 Systems were shipped. The actual number manufactured maybe as high as 57 while DEC appears to have kept 1 or possibly 2 PDP-1 systems for internal use. Therefore 53 to 56 PDP-1 systems may have been shipped. Below is an attempt to reconstructed the client list to determine the system count. The following table is being built from:-
DEC maintained a weekly cycle of backing up significant financial records such as Purchase Orders and Invoices to microfilm. There is a chance all the information to acurately recreate the following tables is sitting unscanned in a box.
Warning: Because of my guesstimates there are significant differences from the established references listed above.
| Count | Serial Number | Customer | Location | Date | Comment | |
|---|---|---|---|---|---|---|
| 1 | PDP-1A | Digital Equipment Corporation | Home Office, Maynard, Mass. | December 1, 1959 | Engineering prototype announced at Boston. | |
| Information International, Inc | July 1963 | Initially installed in the DEC offices then moved to I.I.I. | ||||
| 2 | PDP-1B-1 | Bolt, Beranek and Newman, Inc. | Research Laboratory, Cambridge, Massachusetts | BB&N donated | ||
| University of Massachusetts Amherst. | July 1963 | Initially installed in the BB&N offices. | ||||
| 3 | PDP-1C-1 | Itek Corporation | Lexington, Massachusetts | June 22, 1961 |
| |
| Unknown | 1962 | Itek sold the entire subdivision to Control Data Corporation (CDC). So far no record found regarding ownership of PDP-1 system. | ||||
| 4 | PDP-1C-2 (ADX) | International Telephone and Telegraph Corporation | ISD, New Jersey | 08/28/1961 | ADX-0 Prototype. | |
| State Department, USA | Paris Embassy, France. | ADX-0 Prototype. | ||||
| 5 | PDP-1C-3 | Atomic Energy of Canada Limited | Chalk River Nuclear Laboratories (CRL - CSML) | 02/9/1962 | Chalk River Spectrometer Main Language control system. Refer to Instrumentation Techniques in Nuclear Pulse Analysis 1964, Chapters I-4 and IV-6. | |
| 6 | PDP-1C-4 | Atomic Energy of Canada Limited | Chalk River Nuclear Laboratories (CRL - CSML) | 02/19/1962 | Chalk River Spectrometer Main Language control system. Refer to Instrumentation Techniques in Nuclear Pulse Analysis 1964, Chapters I-4 and IV-6. | |
| 7 | PDP-1C-5 | Massachusetts Institute of Technology | Research Laboratory of Electronics (MIT RLE) | 9/1/1961 | Refer to the Reading Machine for the blind. | |
| 8 | PDP-1C-6 | Atomic Energy of Canada Limited | Chalk River Nuclear Laboratories (CRL - OAL) | 10/1/1961 | ||
| 9 | PDP-1C-7 | Bolt, Beranek and Newman, Inc. | Los Angeles | 11/20/1961 | The PDP-1 Serial Numbers List has the first BB&N system entry as BB&N LA (Los Angeles). but Ken Olsen's memo states this was the second BB&N PDP-1 system. Refer to PDP-1B-1 | |
| 10 | PDP-1C-8 (ADX) | International Telephone and Telegraph Corporation | ADX-1 | 12/15/1961 | ||
| 11 | PDP-1C-9 | Geotechnical Corporation | 12/15/1961 | Earthquake analysis | ||
| 12 | PDP-1C-10 (ADX) | International Telephone and Telegraph Corporation | ADX-2 | 1/15/1962 | ||
| 13 | PDP-1C-11 | Bolt, Beranek and Newman, Inc. | Cambridge | 2/15/1962 | ||
| 14 | PDP-1C-12 | Lawrence Radiation Laboratory | 02/8/1962 | |||
| 15 | PDP-1C-13 | Jet Propulsion Laboratory | Ranger Program. Initial processing of tracking telemetry from the U.S. Mariner 2 space probe during its historic mission to Venus in 1962. | |||
| 16 | PDP-1C-14 (ADX) | International Telephone and Telegraph Corporation | ADX-3 | Guesstimate | ||
| 17 | PDP-1C-15 | Beckman Instruments, Inc. | Beckman Systems Division | 2/2/1962 | ||
| 18 | PDP-1C-16 | Beckman Instruments, Inc. | Beckman Systems Division | 4/18/1962 | ||
| 19 | PDP-1C-17 | Systems Research Laboratories Inc. | 2/20/1962 | |||
| 20 | PDP-1C-18 (ADX) | International Telephone and Telegraph Corporation | ADX-4 | Guestimate | ||
| 21 | PDP-1C-19 (ADX) | International Telephone and Telegraph Corporation | ADX-5 | 5/??/1962 | ||
| 22 | PDP-1C-20 | Digital Equipment Corporation | ||||
| 23 | ? | Unknown | ||||
| 24 | PDP-1C-22 | Charles W. Adams Associates | Better known as Adams Associates. Electronic Drafting Machine (EDM). | |||
| 25 | ? | Unknown | ||||
| 26 | PDP-1C-24 | United Aircraft | ||||
| 27 | PDP-1C-25 | Minneapolis-Honeywell Regulator Company | ||||
| 28 | PDP-1C-26 | Massachusetts Institute of Technology | ||||
| 29 | PDP-1C-27 | Atomic Enery of Canada Limited | Chalk River Nuclear Laboratories (CRL - AECL) | |||
| 30 | PDP-1C-28 | Rutgers University | Loan PDP-1 computer was replaced by a PDP-6 computer in 1965 | |||
| 31 | PDP-1C-29 | Jet Propulsion Laboratory | Supersonic and Hypersonic Wind Tunnels | |||
| 32 | PDP-1C-30 | System Development Corporation | Front-end for the AN/FSQ-32 mainframe. | |||
| - | PDP-1C-31 | Not Built | ||||
| - | PDP-1C-32 | Not Built | ||||
| 33 | PDP-1C-33 | University of Michigan | ||||
| 34 | PDP-1C-34 | Charles W. Adams Associates | 11/2/1962 | Better known as Adams Associates. | ||
| 35 | PDP-1C-35 | National Security Agency | Fort George G. Meade, Maryland | 11/21/1962 | ||
| 36 | PDP-1C-36 | CRBG Hanscom Field Bedford, Massachusetts. | 12/10/1962 | CRBG is probably a designated area within the Cambridge Research Laboratory, Electronic Systems Division, Air Force Systems Command, Hanscom Air Force Base adjacent to Hanscom Field Bedford, Massachusetts | ||
| 37 | PDP-1C-37 | Massachusetts Institute of Technology | MIT Lincoln Laboratory, Hanscom Air Force Base adjacent to Hanscom Field Bedford, Massachusetts | Bedford, Massachusetts03/5/1963 | ||
| 38 | PDP-1C-38 | Raytheon Company | Wayland | 2/28/1963 | Flight simulator | |
| 39 | PDP-1C-39 | Stanford University | 04/30/1963 | |||
| 40 | PDP-1C-40 | Massachusetts Institute of Technology | Project MAC | 04/29/1963 | There is a reference to Inforonics Inc for this system serial number but they initially rented time on a PDP-1 at DEC, refer to PDP-1C-56. | |
| 41 | PDP-1C-41 | Harvard University | Aiken Computation Laboratory (AEC) | |||
| 42 | PDP-1C-42 | Yale University | 06/26/1963 | Bubble Chamber Measurements. | ||
| 43 | PDP-1C-43 | Princeton University | 06/27/1963 | |||
| 44 | PDP-1C-44 | Holloman Air Force Base | Holloman AFB appears to be sometimes misspelled as Hollman Air Force Base. | |||
| 45 | PDP-1D-45 | Bolt, Beranek and Newman, Inc. | ||||
| 46 | PDP-1C-46 | Beckman Instruments, Inc. | Beckman Systems Division | |||
| 47 | PDP-1C-47 | Beckman Instruments, Inc. | Beckman Systems Division | |||
| 48 | PDP-1D-48 | Stanford University | Stanford Artificial Intelligence Laboratory (SAIL) | |||
| 49 | PDP-1C-49 (ADX) | International Telephone and Telegraph Corporation | ADX-10 | |||
| 50 | PDP-1C-50 (ADX) | International Telephone and Telegraph Corporation | ADX-9 | |||
| 51 | PDP-1C-51 | Information International, Inc | ||||
| 52 | PDP-1C-52 (ADX) | International Telephone and Telegraph Corporation | ADX-11 | |||
| 53 | PDP-1C-53 | Massachusetts Institute of Technology | Fort George G. Meade, Maryland | There is a reference that this system was allocated to the National Security Agency which shared this location. | ||
| 54 | PDP-1C-54 | Information International, Inc | ||||
| 55 | PDP-1C-55 | Inforonics |
A single engineering prototype was constructed and has been designated PDP-1A. While the very earliest documentation provides a good introduction to the system that documentation is incomplete with differences from the PDP-1C production version currently emulated by the PiDP-1.
The initial production run was limited to two (2), first run PDP-1 commercial system which were supplied to:-
As these were the next configuration manufactured these two systems are designated as PDP-1B. In DEC Memorandum the Itek system is listed as Serial Number PDP-1C-1 and their PDP-1B is stated to have had two 2 instructions added which may have been the conversion to a PDP-1C.
The production version released by DEC is designated the PDP-1C. The most complete set of historical documentation is available for this version. The only surviving PDP-1C systems are held in the computerhistory.org/exhibits/pdp-1/. This PDP-1C instruction set is the starting point for the PiDP-1 replicas.
Early customers for the PDP-1C included:=
Early customers like BB&N started the process of extending their systems that also resulted in conversion of two PDP-1C systems into PDP-1D systems.
Unfortunately the documentation for all these PDP-1 variants and their hardware is incomplete.
ITT's Automated Data Exchange ADX 7300 used a modified PDP-1C system. DEC received a relatively large order for twelve (12) of this variant of the PDP-1C system with a specific hardware configuration and instruction set. The records indicate twelve (12) ADX 7300 systems were shipped. The PDP-1C (ADX) serial numbers were ADX-0 for the initial machine which was the system installed in the Paris Embassy, France. ADX systems numbered from ADX-0 to ADX-11 being the last system shipped. All DEC identification labelling was stripped. ITT resold the systems under the ITT brand then maintained the ADX 7300 systems. Faulty modules were returned by ITT to DEC for repair under warranty. Therefore DEC did not keep track of theses ITT customers. In the DEC system records they were simply listed as Unknown.
Lost within the following system list are the Three (3) missing PDP-1C (ADX) systems (ADX-6, 7 and 8). PDP-1 #52 system would have been the final system delivered on the ITT contract for 12 PDP-1C (ADX) systems.
ITT cancelled 3 ADX systems and DEC calculated a cancellation charge. Further research required.
Over time BB&N extended the capabilities of their PDP-1C into a configuration that was designated as a PDP-1D system. DEC then sold one (1) PDP-1 system to Stanford University that DEC designated/described as a PDP-1D system. Therefore DEC only ever sold one (1) PDP-1D system. Although the Stanford system was based upon the BB&N PDP-1D configuration, the Stanford system did not implement all the opcodes that had been implemented on the BB&N PDP-1D. As there are implementation differences between these two sites there are in effect two different variants of the PDP-1C systems designated as PDP-1D.
MIT created a radically revised system hardware and instruction set which has been designated PDP-1X. The modifications from the PDP-1C are so radical that the PDP-1X is not universally accepted as a PDP-1 systems.
A PDP-1 can be emulated on a modern PC using The Open SIMH Project computer simulator without any additional hardware. All that is required is a video display, keyboard and mouse. It is possible to write and debug PDP-1 programs without access to a real or replica hardware of a PDP-1 system.
In computer jargon, blinkenlights are diagnostic lights on front panels of old computers. Wikipedia provides an explanation for the term Blinkenlights. Please refer to the Wikipedia article for the complete explanation.
The term has its origins in hacker humor and is taken from a famous (often blackletter-Gothic) mock warning sign written in a mangled form of German. Variants of the sign were relatively common in computer rooms in English-speaking countries from the early 1960s. One version read:-
On the PDP-1's console there are also switches for programming and controlling the system. At approximately 2/3rd size the PiDP-1 Console emulates a PDP-1C system with a complete set of Blinkenlights and switches.
Significant capability has been incorporated into the PiDP-1 Replica after the Obsolecence Guaranteed software was forked. Refer to Bill E's Github documentation for details.
Ignoring the early protoype (PDP-1A) and initial, limited rum, commercial systems (PDP-1B) there are the following variants of PDP-1 instruction sets:-
Documents from different sources may use mnemonics associated with one or more of these different instruction sets. This site is my attempt to track down the mnemonics for all these different instruction sets. There might be a side benefit for people designing custom PiDP-1 modifications when they have to choose their mnemonics to have a reference source. When scanning the available literature I’ve attempted to document every mnemonic and machine code instruction for the PDP-1C and PDP-1D models as a time sharing operating system may require some or all the additional PDP-1D instructions. Documentation for some PDP-1X instructions provided useful for descriptions for some micro-program and IOT instructions. Unfortunately at this point I don’t know which PDP-1X instructions should have been listed as PDP-1D or PDP-1C instructions e.g. micro-program and IOT instructions.
The main areas with missing or incomplete instructions are the Shift/Rotate and Microprogram instructions for the PDP-1X. The other area is I/O peripherals. More research should enable a more complete listing.