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Programmed Data Processor (PDP) was a series of minicomputers made and marketed by the Digital Equipment Corporation from 1957 to 1990. 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 (especially Georges Doriot) would not support Digital's attempting to build a "computer"; the word "minicomputer" had not yet been coined. So instead, Digital used their existing line of logic modules to build a Programmable Data Processor and aimed it at a market which could not afford the larger computers.
The various PDP machines can generally be grouped into families based on word length.
PDP series 
Members of the PDP series include:
- 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 video games, Spacewar!, was developed for this machine.
- An unbuilt 24-bit design.
- First 36-bit machine DEC designed, though DEC did not offer it as a product. The only PDP-3 was built by the CIA's Scientific Engineering Institute (SEI) in Waltham, MA to process radar cross section data for the Lockheed A-12 reconnaissance aircraft in 1960. Architecturally it was essentially a PDP-1 stretched to 36-bit word width.
- Supposed to be a slower, cheaper alternative to the PDP-1, but not commercially successful; all later 18-bit PDP machines (7, 9 and 15) were based on its instruction set. One customer of these early PDP machines was Atomic Energy of Canada. The installation at Chalk River, Ontario included an early PDP-4 with a display system and a new PDP-5 as interface to the research reactor instrumentation and control.
- DEC's first 12-bit machine. Introduced the instruction set later used in the PDP-8.
- 36-bit timesharing machine. Very elegant architecture. It was considered a large minicomputer or a mainframe.
- Replacement for the PDP-4; DEC's first wire-wrapped machine. The first version of Unix was for this machine, as was the first version of MUMPS.
- 12-bit machine with a tiny instruction set; DEC's first major commercial success and the start of the minicomputer revolution. 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.
- A hybrid of the LINC and PDP-8 computers; two instruction sets. Progenitor of the PDP-12.
- Successor to the PDP-7, DEC's first micro-programmed machine. It featured a speed increase of approximately twice that of the PDP-7. The PDP-9 was also one of the first small or medium scale computers to have a keyboard monitor system based on DIGITAL's own small magnetic tape units (DECtape). The PDP-9 established minicomputers as the leading edge of the computer industry.
- 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.
- The archetypal minicomputer; a 16-bit machine and another commercial success for DEC. (Also the LSI-11, primarily for embedded systems). The 32-bit VAX series was descended from it, and early VAX models had a PDP-11 compatibility mode. The 16-bit PDP-11 instruction set has been very influential, with processors ranging from the Motorola 68000 to the Renesas H8 and Texas Instruments MSP430, inspired by its highly orthogonal, general-register oriented instruction set and rich addressing modes. The PDP-11 family was extremely long-lived, spanning 20 years and many different implementations and technologies.
- Descendant of the LINC-8. See LINC and PDP-12 User Manual.
- Designation was not used, apparently due to superstition.
- A 12-bit machine intended as an industrial controller (PLC). Later versions (for example, the PDP-14/30) were based on PDP-8 physical packaging technology. I/O was line voltage.
- DEC's final 18-bit machine. It was their only 18-bit machine constructed from TTL integrated circuits rather than discrete transistors, and had an optional integrated vector graphics terminal. Later versions of the system were referred to as the "XVM" family.
- 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.
Related computers 
- 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
- ^ "Announcements from The DEC Connection". The DEC Connection. 2007-02-14. Retrieved 2008-11-24.
- ^ "PDP-8 Frequently Asked Questions". www.faqs.org. 2001-04-08. Retrieved 2008-11-24.
- ^ "PDP-9". Digital Computing Timeline. Computer History Museum. Retrieved 6 March 2013.
- 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.
External links 
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.