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.
18-bit machine intended to be a slower, cheaper alternative to the PDP-1; it was 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.
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 DECmateword processor and the VT-78workstation. 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.
The archetypal minicomputer; a 16-bit machine and another commercial success for DEC. The LSI-11 was a four-chip PDP-11 used primarily for embedded systems. The 32-bitVAX series was descended from the PDP-11, 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 RenesasH8 and Texas InstrumentsMSP430, 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.
Designation was not used, apparently due to superstition.
A machine with 12-bit instructions, intended as an industrial controller (PLC). It had no data memory or data registers; instructions could test Boolean input signals, set or clear Boolean output signals, jump conditional or unconditionally, or call a subroutine. 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 TTLintegrated 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.
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).
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.