Bob Adamson's PDP-8 PageMy PDP-8/E Restoration Log
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.
PDP-8 Model Availability
From - To
|PDP-5||1963-67||116||???||Transistor||Not strictly a PDP-8 but its main predecessor|
|PDP-8||1965-69||1450||18500||Transistor||Introduction (22nd March)|
|LINC-8||1966-69||142||38500||Transistor||Combination LINC and PDP-8 for laboratory use|
|PDP-8/S||1966-70||1024||10000||Transistor||Serial logic intended to reduce cost but painfully slow as a result|
|PDP-8/I||1968-71||3698||12800||TTL SSI||Used TTL to reduce costs|
|PDP-8/L||1968-71||3902||8500||TTL SSI||Similar to 8/I. Restricted expansion capability|
|PDP-12||1969-73||3500||27900||TTL SSI||Replacement for LINC-8|
|PDP-8/E||1970-78||10000+||6500||TTL MSI||Introduction of Omnibus backplane and TTL MSI|
|PDP-8/F||1972-78||10000+||<5000||TTL MSI||Based on 8/E. Restricted expansion capability|
|PDP-8/M||1972-78||10000+||<5000||TTL MSI||OEM version of 8/F|
|PDP-8/A||1975-84||10000+||1317||TTL LSI||Omnibus, Optional LSI or 8/E cpu|
|VT78||1978-80||???||7995||Microprocessor||Personal Computer using Intersil 6100 cpu|
|DECmate I||1980-84||???||???||Microprocessor||Personal Computer using Harris 6120 cpu|
|DECmate II||1982-86||???||1435||Microprocessor||Personal Computer using Harris 6120 cpu|
|DECmate III||1984-90||???||2695||Microprocessor||Personal Computer using Harris 6120 cpu|
|DECmate III+||1985-90||???||???||Microprocessor||Personal Computer using Harris 6120 cpu|
General information about the PDP8 family of machines is contained in the general FAQ maintained by Douglas Jones. Available from:
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:
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.
PDP-8s are still objects of affection to a small band of enthusiasts and some semi-obligatory links follow here:
Page last updated by on 26th July 2015