Bob Adamson's PDP-8 Page

The DEC (Digital Equipment Corporation) PDP-8 computer was introduced on March 22, 1965 and continued in production until under pressure from the IBM PC the last of the line, the DECmate III, was discontinued 1990. It was by some margin the least expensive parallel general purpose computer on the market and the first computer to be sold on a retail basis. Without doubt it was the most important computer of the 1960's and its low cost opened up the possibility of ownership to a wide range of laboratories and educational institutions, and substantially created the concept of economic computer-controlled machinery. By the mid 1970's the PDP-8 in its various models and configurations had become the best-selling computer in the world, rapidly raising Digital Equipment Corporation (DEC) to a position of eminence amongst computer manufacturers worldwide.

The name PDP-8 derived from DEC's decision to call their range of computers 'Programmed Data Processors' rather than 'computers' which at the time had a reputation for being large, costly and of low sales volumes. DEC needed to raise venture capital and market was wary of computers, so Ken Olsen chose a name which seemed less esoteric. The -8 had no particular significance, being the 8th designed model though DEC's first major commercial success. The term 'minicomputer' was to come years later.

General information about the PDP8 family of machines is contained in the general FAQ maintained by Douglas Jones. Available from:

http://www.cs.uiowa.edu/~jones/pdp8/faqs/

Specific information about each PDP-8 model is contained in the models and options FAQ maintained by Douglas Jones. Taken together, this information constitutes a fairly complete history of the PDP-8; this is available from:

http://www.cs.uiowa.edu/~jones/pdp8/models/

My own introduction to the PDP8 came in about 1969 when I was working for Hughes Aircraft Company in Glenrothes, Scotland. I had joined a new division which was set up to design and manufacture MOS integrated circuits and the division's first integrated circuit tester (from LSI Testing Inc. of Utah if I remember correctly) came complete with a PDP-8/L as its controller. There were no other computers on the site and few people with any programming know-how but fortunately the machine initially had plenty of time on its hands, was well-equipped with the copious DEC documentation and was an irresistible source of interest to we engineers. I learned to program it in assembler and FOCAL and became an instant convert. In due course the 8/L gave way to an 8/I with more memory (see opposite) and since the machine spent a tiny proportion of its time controlling the tester it became possible to modify the software to allow timesharing between the tester and a single-user running FOCAL.

At university in Edinburgh the computer science department acquired an 8/E (see opposite) which it made available to students for hands-on experience. This machine had a DF32 hard disk and could run DEC's Disk Monitor operating system. It was allocated a small room of its own in an alleyway in the Grassmarket leading to the computer centre and I more or less took up residence there in my spare hours. Post-university, Hughes bought an 8/E and some 8/A computers both for general laboratory use and to control test gear and they became a significant part of my engineering life until I moved away to another job where DEC VAXs (Vaxen?) ruled and PDP8s were not heard of. I built a home-made computer based on the Intersil IM6100 chip set (this was something of a mistake as the I/O incompatibilities with a standard PDP8 made it a nightmare). Much more recently I have built a board based on the Harris HD6120 followup chip which is a very close fit to the 8/e and which can run OS/8 on an IDE drive.

Around 1998 I decided to begin a new hobby prompted by the discovery and acquisition of a couple of PDP-8/Is from a local university Shortly after that I received a reply to semiregular messages which I had been posting on newsgroups in search of a PDP-8/E. In a surprising coincidence another ex-Hughes employee recognised my name and turned out to have a couple of the original Hughes PDP-8s which he had obtained when they were scrapped. He wanted to dispose of them and so I now have an ex-Hughes PDP-8/E and PDP-8/A (see opposite) in my collection. As a final twist to the tale, on opening the 8/E I was surprised to find two wire-wrapped boards which I'd designed in about 1977 still plugged into the omnibus. Later still I obtained another 8/E from a contact at a local university. Sadly the original 8/Is have had to go after I retired and moved to a smaller house but I still have the 8/Es and 8/A (though this is a whole lot less interesting as by then DEC had begun to respond to the need for a cheaper and therefore lower-quality build). I plan to add a few pages to this site as I refurbish these old computers which haven't been turned on for over 20 years. In fact the ex-Hughes PDP-8/E is now up and running again some 30 years after it was decommissioned.

• Restoring a PDP-8/E

PDP-8s are still objects of affection to a small band of enthusiasts and some semi-obligatory links follow here:

• Douglas W Jones has created the authoritive PDP-8 FAQ. He has also created a *nix emulator.

• David Gesswein has a fine collection of machines and his site contains a large amount of DEC software and documentation. It includes a PDP-8 which can be run on-line.
• Kevin McQuiggin's 'Highgate' site contains considerable software and documentation.
• Aaron Nabil has a small set of pages with some important documentation.
• The Bitsavers site has a huge selection of PDP-8 documentation including scans of several of DEC's unusually detailed handbooks.
• Bob Supnik's Computer History Simulation Project contains quality emulators and software packages for many machines including the PDP-8 range. Both Windows and *nix are supported and in particular a wide range of peripherals.
• Bob Armstrong's Sparetimegizmos site contains a good Windows-based emulator and details of a single-board PDP-8 act-alike based on the Harris HD6120 chip (I've built one and it all works just fine).
• Robert Krten's 'museum' contains a selection of machines and a writeup on how he restored an old PDP-8/I computer. The museum itself has moved on now but the pages have been preserved by another enthusiast.
• The PDP-8 archive at www.ibiblio.org  contains a useful collection of software for the PDP-8.
• Paul Pierce's PDP-8 Family page , part of his huge collection, has some good photographs of his machines though it is short on technical detail.
• Toby Russell's PDP-8 site. Toby majors in PDP-11s but he also has a nice collection of 8s.
• Willem van der Mark has written an interesting Java emulator for the PDP-8/E. Restricted to the range of peripherals of his own machine and slightly non-DEC, but very friendly to use.
• For Apple MacIntosh afficionados Bernhard Baehr has written a superb emulator.
• The Vintage Computer Forum has an active DEC section.

Page last updated by on 26^th July 2015