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The PDP-11 is a series of minicomputers introduced in 1969 [1] by the Digital Equipment Corporation (DEC), in production by them from 1970-1990. Their life-time spanned a period of momentous changes in the computer world: when they were first introduced (and for a little less than half their life), core memory was still the standard main memory technology; by the end, microprocessors had become ubiquitous.

Front panel of the KA11, the first PDP-11 model

The machine word size was 16 bits, and it was a general register architecture. Although it was not the first to feature the latter, its wide distribution (in 1980, it was the world's best-selling computer) has helped influence almost all later machines to follow that path.

(For more information about the architecture, including its innovative and much-copied stack-oriented addressing modes, see PDP-11 architecture.)

PDP-11's came in two groups: those which used the UNIBUS for a bus, and the later ones which used the QBUS. Eventually DEC stopped producing UNIBUS PDP-11's (the last were the PDP-11/44 and PDP-11/24); later 'UNIBUS' machines (the PDP-11/84 and PDP-11/94) actually contained QBUS processors with a QBUS<->UNIBUS adapter board.

Towards the end of its life, there were several microcomputer implementations of the PDP-11, as chips.

It could run a variety of operating systems. Many were produced by DEC themselves, but several were produced by third-parties. It was the machine which made UNIX, which now seems to have taken over the world (in the form of Linux) widely known and popular, with UNIX Sixth Edition. Often DEC would purchase or re-brand such an OS and re-sell it as their own product; for example, UNIX sold as Ultrix by DEC.

After DEC discontinued production of PDP-11's, the line was sold to Mentec, who produced a few newer models.

Operating Systems

Unix based Operating Systems

These are the original Bell Laboratories releases of Unix; the first 4 were only internal to Bell, the Fifth saw limited distribution outside it, and the Sixth took over the world.

This was the first shipping Unix distro by AT&T. It only supported the PDP-11 and VAX computers.

This version was a port of the 4.3 BSD feature set to the PDP-11. Although considered impossible by many, it accomplished this by using overlays for portions of the kernel, and to allow for user programs larger then 64kb.

This version is still supported, and if one really felt the need to load a Unix for use on a PDP-11 this would be the best fit. It has support for TCP/IP, large memory space and is the best UNIX experience one can get going to get on a 16-bit mini.

Other OS's

Technically also an OS is XXDP, which is an 'overseer' for running the PDP-11 diagnostics produced/provided by DEC.

PDP-11 Models and notes

Model Introduced Bus Type Addressing Notes Speed (VUPS)
11/20 1969[1] UNIBUS 16-bit
11/05 1972 UNIBUS 16-bit OEM model
11/10[*] 1972 UNIBUS 16-bit
11/15 1972 UNIBUS 16-bit OEM model
11/35 1973 UNIBUS 18-bit OEM model
11/40 1973 UNIBUS 18-bit
11/45 1973 UNIBUS 18-bit core memory
11/50 1975 UNIBUS 18-bit MOS memory
11/55 1976 UNIBUS 18-bit fast bipolar memory
11/70 1975 UNIBUS 22-bit 0.6
11/03 1975 QBUS 16-bit first QBUS model 0.5
11/04 1976 UNIBUS 16-bit 0.11
11/34 1976 UNIBUS 18-bit 0.21
11/60 1977 UNIBUS 18-bit writable control store
11/23 1979 QBUS 18-bit or 22-bit first F-11 0.12
11/24 1979 UNIBUS 22-bit only UNIBUS model to use F-11 chip 0.18
11/44 1979 UNIBUS 22-bit last non-LSI PDP-11 0.42
11/23+ 1981 Nov QBUS 22-bit 0.18
11/73 1983 QBUS 22-bit first J-11 machine, 15MHz, integrated FPU, also first PMI PDP-11 0.45
11/53 1984 QBUS 22-bit S-box or standard QBUS, integrated FPU, 768KiW memory 0.29
11/83 1988 QBUS 22-bit J-11 at 18MHz, integrated FPU 0.72
11/84 1988 UNIBUS 22-bit J-11 at 18MHz, integrated FPU 0.72
11/93 1990 QBUS 22-bit J-11 at 18MHz, integrated FPU, 2MiW onboard memory 1.0
11/94 1990 UNIBUS 22-bit J-11 at 18MHz, integrated FPU, 2MiW onboard memory 1.0

[*]The name PDP-11/10 was recycled by DEC from an earlier KA11 CPU-based 11/10 from 1969, or at least it existed in advertisements[1]

See also

External links