Programmed Data Processor


Programmed Data Processor, referred to by some customers, media and authors as "Programmable Data Processor," is a term used by the Digital Equipment Corporation from 1957 to 1990 for several lines of minicomputers.
The name "PDP" intentionally avoids the use of the term "computer". At the time of the first PDPs, computers had a reputation of being large, complicated, and expensive machines. The venture capitalists behind Digital would not support Digital's attempting to build a "computer" and the term "minicomputer" had not yet been coined. So instead, Digital used their existing line of logic modules to build a Programmed Data Processor and aimed it at a market that could not afford the larger computers.

Familes

The various PDP machines can generally be grouped into families based on word length and backward compatibility. Families of PDP machines include:
;PDP-1: The original PDP, an 18-bit four-rack machine used in early time-sharing operating system work, and prominent in MIT's early hacker culture, which led to the Route 128 hardware startup belt. What is believed to be the first video game, Spacewar!, was developed for this machine, along with the first known word processing program for a general-purpose computer, "Expensive Typewriter". It was based to some extent on the TX-0 which Ben Gurley had also contributed to. His engineering requirement was to build it from inventory.
;PDP-2: A number reserved for an unbuilt, undesigned 24-bit design.
;PDP-3: First DEC-designed 36-bit machine, though DEC did not offer it as a product. The only PDP-3 was built from DEC modules by the CIA's Scientific Engineering Institute in Waltham, Massachusetts to process radar cross section data for the Lockheed A-12 reconnaissance aircraft in 1960. Architecturally it was essentially a PDP-1 controlling a PDP-1 stretched to 36-bit word width.
;PDP-4: This 18-bit machine, first shipped in 1962 of which "approximately 54 were sold" was a compromise: "with slower memory and different packaging" than the PDP-1, but priced at $65,000 - considerably less than its predecessor. It was not compatible with the PDP-1. All later 18-bit PDP machines are based on a similar, but enlarged instruction set, more powerful, but based on the same concepts as the 12-bit PDP-5/PDP-8 series. 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.
;PDP-5: It was the world's first commercially produced minicomputer and DEC's first 12-bit machine. The instruction set was later expanded in the PDP-8 to handle more bit rotations and to increase the maximum memory size from 4K words to 32K words. It was one of the first computer series with more than 1,000 built.
;PDP-6: This 36-bit machine, DEC's first large PDP computer, came in 1964 with the first DEC-supported timesharing system. 23 were installed. Although the PDP-6 was "disappointing to management," it introduced the instruction set and was the prototype for the far more successful PDP-10 and DEC System-20, of which hundreds were sold.
;PDP-7: Replacement for the PDP-4; DEC's first wire-wrapped machine using the associated Flip-Chip module form-factor. It was introduced in 1964, and a second version, the 7A, was subsequently added. A total of 120 PDP-7 and PDP-7A systems were sold.
;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.
;LINC-8: The system contained both a PDP-8 CPU and a LINC CPU; two instruction sets; 1966. Progenitor of the PDP-12.
;PDP-9: Successor to the PDP-7; DEC's first micro-programmed machine. It features a speed increase of approximately twice that of the PDP-7. The PDP-9 is 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. The PDP-9 established minicomputers as the leading edge of the computer industry.
;PDP-10: Also marketed as the DECsystem-10, this 36-bit timesharing machine was quite successful over several different implementations and models. The instruction set is a slightly elaborated form of that of the PDP-6.
;PDP-11: The archetypal minicomputer ; a 16-bit machine and another commercial success for DEC. The LSI-11 is a four-chip PDP-11 used primarily for embedded systems. The 32-bit VAX series is descended from the PDP-11, and early VAX models have 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.
;PDP-12: 12-bit machine, descendant of the LINC-8 and thus of the PDP-8. It had one CPU that could change modes and execute the instruction set of either system. See LINC and . With slight redesign, and different livery, officially followed by, and marketed as, the "Lab-8".
;PDP-13: Designation was not used.
;PDP-14: A machine with 12-bit instructions, intended as an industrial controller. It has no data memory or data registers; instructions can test Boolean input signals, set or clear Boolean output signals, jump conditional or unconditionally, or call a subroutine. Later versions are based on PDP-8 physical packaging technology. I/O is line voltage.
;PDP-15: DEC's final 18-bit machine. It is the only 18-bit machine constructed from TTL integrated circuits rather than discrete transistors, and, like every DEC 18-bit system has an optional integrated vector graphics terminal, DEC's first improvement on its early-designed 34n where n equalled the PDP's number. Later versions of the PDP-15 run a real-time multi-user OS called "XVM". The final model, the PDP-15/76 uses a small PDP-11 to allow Unichannel peripherals to be used.
;PDP-16: A "roll-your-own" digital system using Register Transfer Modules, mainly intended for industrial control systems with more capability than the PDP-14. They could be used to design a custom controller consisting of a control structure and associated data storage and manipulation modules, or to design a small computer which could then be programmed. The PDP-16 modules were based on the RTMs designed by Gordon Bell during his time at CMU. The PDP-16/M was introduced in 1972 as a pre-assembled set of the PDP-16 modules that could be programmed and was nicknamed a "Subminicomputer".

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. When the memory was replaced with a smaller one, the instruction set was expanded, and it was moved to the MIT campus. When a PDP-1 arrived on campus, it was placed in the next room. Software such as an assembler was ported from the TX-0 to the PDP-1 and the machines were connected for communications between them.
  • LINC, 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 are 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.
  • Several unlicensed clones of the PDP-11.
  • TOAD-1 and TOAD-2, Foonly, and Systems Concepts PDP-10/DECSYSTEM-20-compatible machines.