Bob Adamson's PDP-8 Page

The DEC 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.

PDP-8 Model Availability
Model Production
From - To		 Approximate
Number Built		 Price $ Technology Comments
PDP-5 1963-67 116 ??? Transistor Not strictly a PDP-8 but its main predecessor
PDP-8 1965-69 1450 18500 Transistor Introduction
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 alt.sys.pdp8 general FAQ. This is available from any of the following:

The Ohio State WWW site (recommended)
www.faqs.org (recommended)
The Usenet FTP archive (plain text)

Specific information about each PDP-8 model is contained in the alt.sys.pdp8 models and options FAQ. Taken together, this information constitutes a fairly complete history of the PDP-8; this is available from any of the following:

The Ohio State WWW site (recommended)
www.faqs.org (recommended)
The UNC PDP-8 FTP archive (plain text and out of date)

Front view of a DEC PDP8/I computer consoleMy 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 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.

Front view of a DEC PDP-8/E computer console At university in Edinburgh the computer science department acquired an 8/E 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.

Front view of a DEC PDP-8/A computer consoleAround 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 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. PDP-8s are still objects of affection to a small band of enthusiasts and the semi-obligatory links follow here:

Page last updated by on 30th September 2011