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)
Specification - PDP-11/20
(56 K bytes maximum)
Initially, symbolic editor,
debugger, utilities, PAL
Became industry standard for
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
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
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
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
1887 MicroPDP-11/53 +
1990 MicroPDP-11/93, MicroPDP-11/94