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Programmed Data Processor (abbreviated PDP) was the name of a series of minicomputers, several of them ground-breaking and very influential, made by Digital Equipment Corporation. The name 'PDP' intentionally avoided the use of the term 'computer' because at the time of the first PDPs, computers had a reputation of being large, complicated, and expensive machines, and the venture capitalists behind Digital (esp. Georges Doriot) wouldn't support Digital's attempting to build a "computer". The word "minicomputer" was not invented yet. So instead, Digital used their existing line of logic modules to build a Programmable Data Processor and aimed it at a market which couldn't afford the larger computers.

The various PDP machines can generally be grouped into families based on word length. With the notable exception of the 16-bit PDP-11, the various architectures all show strong similarities, with the 36-bit PDP-6 and PDP-10 architecture being the most elaborate version.

PDP-11/04 or 11/34 with RK05 moving-head disk drive, RX01/2 dual 8" diskette drive, and third-party magnetic tape drive.

Members of the PDP series include:

• PDP-1: The original PDP, an 18-bit machine used in early time-sharing operating system work, and prominent in early hacker culture. One of the first computer games, Spacewar!, was developed for this machine.
• PDP-2: an unbuilt 24-bit design.
• PDP-3: First 36-bit machine DEC designed, though DEC did not offer it as a product. The only PDP-3 was built by a customer (alleged to be an intelligence agency) in 1960. Architecturally it was essentially a PDP-1 stretched to 36-bit word width.
• PDP-4: Supposed to be a slower, cheaper alternative to the PDP-1, but not commercially successful; all later PDP 18-bit machines were based on its instruction set.
• PDP-5: DEC's first 12-bit machine. Introduced the instruction set later used in the PDP-8. As a cost-saving measure, the memory location at address zero was used as the program counter, rather than the more typical approach of using a dedicated hardware register. This feature was a debugger's nightmare, because it was so easy to smash the instruction counter.
• PDP-6: 36-bit timesharing machine. Very elegant architecture. It was considered a large minicomputer or a mainframe.
• PDP-7: Replacement for the PDP-4; DEC's first wire-wrapped machine. The first version of Unix was for this machine.
• PDP-8: 12-bit machine with a tiny instruction set; DEC's first wildly successful computer. The first successful "personal computer" or minicomputer, many were purchased by schools, university departments, and research laboratories. Later models were also used in the DECmate word processor and the VT-78 workstation. It is reported that Edson de Castro, who had been a key member of the design team, left to form Data General when his design for a 16-bit successor to the PDP-8 was rejected in favour of the PDP-11; the "PDP-X" did NOT resemble the Data General Nova, although that is a common myth.
• LINC-8: A hybrid of the LINC and PDP-8 computers; two instruction sets. Progenitor of the PDP-12.
• PDP-9: Successor to the PDP-7, DEC's first micro-programmed machine.
• PDP-10: 36-bit timesharing machine, and fairly successful over several different models. The instruction set was a slightly elaborated form of that of the PDP-6.
• PDP-11: The archetypal minicomputer; a 16-bit machine, widely regarded as the best 16-bit instruction set ever created, and another huge hit for DEC. (Also the LSI-11, primarily for embedded systems). The 32-bit VAX series was descended from and mostly backwards-compatible with it. The PDP-11 instruction set has been immensely influential, with CPUs like the Motorola 68000 right through to the Renesas H8 and Texas Instruments MSP430 adopting its highly orthogonal, general-register oriented instruction set and rich addressing modes. The PDP-11 family was incredibly long-lived, with 20 years and many different implementations and technologies.
• PDP-12: Descendant of the LINC-8. See LINC and PDP-12 User Manual.
• PDP-13 was not used, apparently due to superstition.
• PDP-14: A 1-bit machine intended as an industrial controller (PLC). Latter versions (for example, the PDP-14/30) were based on PDP-8 physical packaging technology. I/O was line voltage.
• PDP-15: DEC's final 18-bit machine. 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.
• PDP-16: A "roll-your-own" sort of computer using Register Transfer Modules, mainly intended for industrial control systems with more capability than the PDP-14. The PDP-16/M was introduced as a standard version of the PDP-16.

• TX-0 designed by MIT's Lincoln Laboratory, important as influence for DEC products including Ben Gurley's design for the PDP-1
• LINC (Laboratory Instrument Computer), originally designed by MIT's Lincoln Laboratory, some built by DEC. Not in the PDP family, but important as progenitor of the PDP-12. The LINC and the PDP-8 can be considered the first minicomputers, and perhaps the first personal computers as well. The PDP-8 and PDP-11 were the most popular of the PDP series of machines. Digital never made a PDP-20, although the term was sometimes used for a PDP-10 running TOPS-20 (officially known as a DECSYSTEM-20).

• SM EVM series of computers in the USSR
• DVK personal computers series are PDP clones developed in USSR in 70s.
• Elektronika BK
• UKNC

This article or section includes a list of references or external links, but its sources remain unclear because it lacks in-text citations. You can improve this article by introducing more precise citations.

• C. Gordon Bell, J. Craig Mudge, John E. McNamara, Computer Engineering: A DEC View of Hardware Systems Design (Digital, 1978)
• The Computer Museum Report, Volume 8, TX-0 alumni reunion, Spring 1984, Ed Thelen Web site (accessed June 18, 2006)
• Bell, C.G., Grason, J., and Newell, A., Designing Computers and Digital Systems. Digital Press, Maynard, Mass., 1972.

Wikimedia Commons has media related to:

Programmed Data Processor

• Mark Crispin's 1986 list of PDP's
• Several PDP and LAB's, still runnable in a German computer museum
• DEC's PDP-6 was the world's first commercial time-sharing system Gordon Bell interview at the Smithsonian
• Description and Use of Register Transfer Modules on Gordon Bell's site at Microsoft.
• www.parse.com/~museum shows a recently restored PDP-12

Various sites list documents by Charles Lasner, the creator of the alt.sys.pdp8 discussion group, and related documents by various members of the alt.sys.pdp8 readership with even more authoritative information about the various models, especially detailed focus upon the various members of the PDP-8 "family" of computers both made and not made by DEC.