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Manufacturer Digital Equipment Corporation (DEC)
Identification,ID PDP-11, LSI-11, many models
Date of first manufacture1973
Number produced -
Estimated price or cost-
location in museum -
donor Bank of America.

Contents of this page:

DEC PDP-11/70


16 bit words, memory mapped I/O (4 K word, LSI-11 used "Q-bus")

6 general registers (16 bit) (Reg 0-5), a Stack Pointer (Reg 6), Instruction Pointer (Reg 7)
(DEC liked to claim 8 general registers, and they were addressed similarily, but you better not add arbitary values to registers 6 & 7)

Instruction List, Page 1, 2, 3, 4, 5, 6, 7, 8, 9

From "Digital at Work" , Digital Press, copyright 1992, page 58

                Specification - PDP-11/20

First shipped
    Spring 1970
Word length
    16 bits
    800 nanoseconds
Primary memory
    Magnetic core
    (56 K bytes maximum)
Instruction set
    Initially, symbolic editor,
    debugger, utilities, PAL
    Became industry standard for
    16-bit minicomputers

A New Architecture

The more people used minicomputers, the more uses they found for them. By the mid-1960s, many customers began to outgrow their machines. As the cost of hardware dropped, the costs of developing software and training rose.

Five years after the success of the PDP-8, Digital engineered anew machine with more power at a lower price. The PDP-11 introduced the idea of compatibility as a safeguard against obsolescence and sold close to a million machines.

By 1971, all the power of a CPU could be packed onto a sliver of silicon.In another year, floppy disks offered a cheap, portable alternative to built-in hard disks, parallel processing presented an alternative to von Neumann's original step-bystep scheme, and relational databases showed the potential of electronic libraries - asthe video game craze emptied pockets of loose change.

By the mid-1970s, computers in medicine performed CAT scans and were used to confirm diagnoses, Wang sold word processing, and the CRAY-1 was the first successful vector processor.

A Lasting Success

From 1970 to 1990, Digital built four generations of PDP-11 systems, ranging from a small 4-user system to a large 64-user machine. In 1975, a new generation of hardware technology, Large Scale Integration (LSI),furtherstreamlined the PDP-11 design. The "computer on a board" provided greater performance than the PDP-11/20 and maintained compatibility with the PDP-11 systems that preceded it.

The PDP-11 was an instant success. In its first week of release Digital received 150 orders. Today more than half a million PDP- 11 systems are still operating around the world.

The phenomenal popularity and growth of the PDP-11 product line led to a change in Digital's organizational structure. As larger and more complex PDP-11 systems were engineered, Digital reorganized product lines to correspond more closely to specific applications and markets.

Much fanfare attended the design and manufacture of the PDP-11. To escape the fire of PDP-9 wire-wrapping guns, the design team worked below the loading dock of the Mill, coming up regularly for design reviews.

                PDP-11 Family Timeline

1970	PDP-11/20, first of the PDP-11 series of
	compatible systems, first UNIBUS product
1972	PDP-11/05, better price/performance for
	OEM low-end requirements
	PDP-11/10, end-user version of 11105, for
	data acquisition and industrial control
	applications PDP-11/45, fastest in its price
	range, uses three types of primary memory
1973	PDP-11/40,PDP-11/35
1974	PDP-11/04
1975	PDP-11/03, LSI-11,"computer on a board"
	incorporates Large Scale Integration (LSI)
	PDP-11/70, internal cache-memory design
1976	PDP-11/34, PDP-11/55
	PDT-11/150, Programmable Data Terminal,
	first terminal-based PDP-11 system, based
	on the LSI-11 board
1977	LSI-11/2: LST-11 in half the size
1978	PDT-11/110, /130, packaged inside the new
	VT100 terminal
1979	F-11 chip set
	MicroPDP-11/23, minicomputer performance
	and software in micro-sized package, runs
	RSX-11M operating system
1981	PDP-11/24, entire computer central processor
	on single 8 x 10 circuit board
	GIGI,low-cost graphics generator uses
	LSI-11 board
	T-11 chip, first chip-level PDP-11
1982	Professional 300,325,350 personal
	computers, the "Personal PDP-11"
	J-ll,a PDP-11/70 in two microprocessor
1983 Micro PDP-11/73
1985 PDP-11/84, Professional 380
1985 MicroPDP-11/83
1986 MicroPDP-11/53
1887 MicroPDP-11/53 +
1990 MicroPDP-11/93, MicroPDP-11/94

Special features
  • The LSI-11 was introduced later. It was a 3 chip set processor that plugged into a Q-Bus, it also required
    • a memory
    • a serial interface card
    to be plugged into the Q-bus
    Oh the LSI-11 card was
    • a big microcode ROM chip
    • a processor chip
    • and an optional Floating Point chip
    • jumper options for starting and power fail
    It did NOT have a front panel with lights and switches. (I felt cheated.) All commands were through a serial interface to a terminal, like a KSR-33, or VT-100.
  • -

Historical Notes
Peter Simpson wrote (September 2004)
Here's a real interesting link - Details on DeCastro's unchosen design for "PDP-X"

Keith wrote (February 2004)
this was the first system to run an AT&T UNIX which was written in C. (C was not available for the PDP-7, but was written by AT&T researchers for the 11.) It was also the PDP-11 on which BSD UNIX was first developed.

This Specimen

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Updated September 13, 2004