Computermuseum der Fakultät Informatik german
Type: PDP8/L <<< *** >>> ^^^
Manufacturer: Digital Equipment Corp.
Magnetic Core Memory 4096W * 12Bit
Price: about DM 50000.-
The PDP-8 computers were the most widely spread minicomputers of the
world. In 1978, DEC was advertising them by having sold 50.000 units
worldwide. The first version, the primary PDP8 was still assembled with
discrete transistors and had the same instruction set like the very
older PDP5. Both have 12Bit words. This comes from the original main
application of the PDP5 as a small process computer, which should
process the data from an analog/digital converter, that was
integrated in the accumulator. All PDP8 commands consist of only one
word. The minimal word length is 12 Bits, which still allows an usable
machine instruction set.
In the course of time, the PDP8 was reimplemented more than 10 times
with the always corresponding semiconductor technology, but the
instruction set stayed effectively unmodified. On this computer-family,
you can clearly see which influence the semiconductor technology has
for the computers with otherwise unmodified conditions. The PDP8/L was
the third reimplementation after the PDP8/S and the PDP8/I.
It was the very smallest computer that an engineer or a scientist could
put on his desktop for personal use. Only a Teletype-machine was
required as a peripheral device, which is described on an other
position here. Because of the core memory of the PDP8/L, programs
have only be loaded once and then stay at the memory after switch-off.
Thus working with the quite slow Teletype was practicable.
The labeling PDP is by the way a mimikry: At the beginning, computers
were considered as extremely expensive devices, which needed much
space and electricity and had to be cooled down complexly. For
operating engineers, programmers and operators were necessary. To
improve the opportunity of sale, DEC didn't name it 'computer' but
'Programmable Digital Processor'(PDP).
Thus the instruction set of the single PDP8-generations always stayed
compatible, by the time real big software pool was accumulated.
This software was traded and distributed by DECUS, the
'DEC User Society'. On the PDP8/L exposed at the museum, in the
4K main memory run for example Focal-69 (an interpreter language),
LISP 1.5, FORTRAN, SPASTC (an emulation of an scientific calculator),
CHECKMO-II (a chess program) as well as various floating point
interpreters. Additional reasons for the popularity of ths computers
was the simple, but though very powerful instruction set as well as
the fact that the hardware was very well-documented by the
manufacturer. In the famous 'Small Computer Handbooks', which came
with every delivered computer, there was a exact manual, how they could
assemble extenstions by themselves, for example to automate theis
measurement setups or their controls in the laboratory or at the
On the left of the picture, the opened PDP8/L can be viewed: On the
top the Wire-Wrap-Field, where the single modules are wired with,
right beside a stack with puncehd tapes, containing the provided
system software, right in the front the 'Small Computer Handbook',
with that you can really understand computers and in front of the
frontpanel two single punched tapes.
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