PDP: Meaning (information, definition, explanation, facts)

PDP is an abbreviation for Programmed Data Processor, the name of a series of computers, several of them ground-breaking and very influential, made by Digital Equipment Corporation. They were given that name because at the time of their introduction, computers had a reputation of being large and expensive machines, and the PDP machines were aimed 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 architectures show strong similarities, with the 36-bit PDP-6 and PDP-10 architecture being the most elaborate.

PDP Series

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-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. Architecturally it was essentially a PDP-1 stretched to 36-bit word width.

• PDP-4: Supposed to be a slower, cleaper 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.

• 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", many were purchased by schools, university depts, and research labs; also used in the DECmate word processor and the VT-78 workstation.

• 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: 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 VAX series was descended from it.

• PDP-12: Descendant of the LINC-8.

• PDP-14: A 12-bit machine intended as an industrial controller.

• PDP-15: DEC's final 18-bit machine. Their only 18-bit machine constructed from TTL integrated circuits rather than discrete transistors.

• 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.

Related computers:

• LINC (Laboratory Instrument Computer), originally designed by MIT's Lincoln Labs, 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.

• C. Gordon Bell, J. Craig Mudge, John E. McNamara, Computer Engineering: A DEC View of Hardware Systems Design (Digital, 1979)