PDP-11

The PDP-11 is a series of computers introduced in 1969 [1] by the Digital Equipment Corporation (DEC), in production there 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.

A loaded QBUS PDP-11/23 PLUS

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.

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 widely known and popular, with UNIX Sizth Edition.) Often DEC would purchase or re-brand this 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

• UNIX First Edition
• UNIX Second Edition
• UNIX Third Edition
• UNIX Fourth Edition
• UNIX Fifth Edition
• UNIX Sixth Edition
• Unix Seventh Edition

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.

• System III

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

• 2.9 BSD

This version was a port of the 4.3 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.

• 2.10 BSD
• 2.11 BSD

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 experence one can get going to get on a 16-bit mini.

Other OS's

• RSX-11
• RSTS/E
• RT-11

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
11/10	1972	UNIBUS	16-bit	KD11-B processor[*]
11/15	1972	UNIBUS	16-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
11/70	1975	UNIBUS	22-bit		0.6
11/03	1975	QBUS	16-bit	first QBUS model, first F-11	0.5
11/34	1976	UNIBUS	18-bit		0.21
11/04	1976	UNIBUS	16-bit		0.11
11/55	1976	UNIBUS	18-bit	fast bipolar memory
11/60	1977	UNIBUS	18-bit	writable control store
11/23	1979	QBUS	18-bit or 22-bit		0.12
11/24	1979	UNIBUS	22-bit	first 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

• PDP-11 Memory Management
• FP11 floating point
• UNIBUS memories
• QBUS memories
• UNIBUS boot ROMs
• QBUS boot ROMs

References

• PDP-11/20 Price List