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Programmed Data Processor (abbreviated PDP) was the name of a series of computers, 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 attempting to build a "computer". So instead, Digital used their existing line of logic modules to build a Programmed 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.
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PDP series
Members of the PDP series include:
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.
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" essentially became the Data General Nova.
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.
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.
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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).
DVK personal computers series are PDP clones developed in USSR in 70s.
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