Digital Equipment Corporation was founded in 1957 in Maynard, Massachusetts. Their first facility was in an old mill, they started with just 3 people. They produced logical modules, core memory testers and other small electronical components, and started to build computers later. In those days the word "computer" referred to a big, power-demanding electrical thing which was way too expensive (more than a million dollars), so DEC decided to name their product "Programmed Data Processor". That was the PDP-1 in 1960. It was small, inexpensive - and successful! By 1961 they sold enough of them to have a solid userbase, which led to the launch of DECUS.

    The PDP-4 was introduced in 1962. (Only one PDP-3 was built by a costumer; the -2 has never been produced) The PDP-5 was a 12 bit computer, launched on year later. The PDP-6 (1964) was 36 bit, and marked the birth of a long line of 36-bit computers form DEC. The 18-bit PDP-7 and the 12-bit PDP-8 hit the market in 1965. The latter proved to be a classic machine: it was inexpensive, compact, it could have been the forerunner of the PC. Later versions of the -8 were manufactured 'til the mid-80's. The -8 was proceeded by the 18-bit PDP-9, and the 36-bit PDP-10. The -10 was another classic, the PDP of the mainframe-class. Later it was renamed to DECsystem-10 and DECSYSTEM-20, both were successful, but in the eighties DEC killed the line in favor of the VAX series. The PDP-12 was introduced in 1969, and in 1970 came the machine this page is all about: the beloved and respected PDP-11. DEC is superstitous, there was no PDP-13. The PDP-14 was a real-time controller, the -15 a successor of the -9, implemented in TTL. The last machine marketed under the name "PDP" was the -16 in 1972.

    After the success of the PDP-8, leading hardware engineer Edson DeCastro designed a 16-bit machine under the codename "PDP-X", which was rejected in favor of another machine, to be known as the PDP-11. DeCastro parted with DEC, and formed Data General. Some say that the misterious PDP-X became the new company's successfull Nova series, other say that the -X was much more complicated than both the Nova and the -11.

The birth of the PDP-11, as remembered by Larry McGowan.

    Anyway, the -11 was one the (if not the) most successful computers of all times. It began its career as a minicomputer, and ended up as a micro or supermicro/supermini. It was manufactured from 1970 to 1990. Members of the -11 line were sold in very high numbers, thanks to the growing OEM industry. The VAX line of DEC began its life as an enhancement to the -11 architecture, the first VAXen are sometimes mentioned as PDP11-7xx, in contrast to the official label VAX-11/7xx...

    About the PDP-11 life-line: one might think, that they're numbered incrementaly, so the 11/20 is newer than the 11/03. Well, that's wrong. I don't know how DEC assigned the numbers to the different series; here are some guidelines: odd numbered earlier -11's are OEM-versions of -11's with even numbers. Thus, the 11/15 is the OEM-version of the 11/20, so is the /35 of the /40. Warning: /45, /50 and /55 are exceptions... The other "rule": newer -11's with odd numbers are qbus (LSI-11 bus) machines, even numbered ones use the UNIBUS (e.g. the 11/83 is qbus, 11/84 is UNIBUS).

    The family tree below gives a hint of the evolution of the -11 family. It's not even near perfect, so any help would be appreciated! Navigation "inside" the tree is not easy: it's not a straight-forward evolution, not every -11 subseries had a predecessor and/or a successor, so there are no "Forward" and "Back" buttons on the pages dedicated to the different models.

My main information sources were: the PDP-11 FAQ, the readers of vmsnet.pdp-11, and the web-pages of computer collectors. The pictures are from Digital's Photo Library, from collectors' web pages, from magazines, newspapers, and there are also some photos taken by me. Special thanks to Zoltan Kovacs and Peter Verhas at Digital Hungary, to Johnny Billquist, Carl R. Friend, Rolf Geert, Megan Gentry, Gerald Goodrich, Jean Huens, Larry McGowan, Paul Pierce, Aki Pursiainen, Steve Rothman, Saku Setala, Csaba Tóth, James Willing, John Wilson, and to the numerous -11 maniacs who helped me!

      Unofficial PDP-11 Family Tree



                     UNIBUS systems                !      Q-BUS systems      !      others 
                                                   !                         !
                                                   !                         !
1969       planing                                 !                         !
                                                   !                         !
1970                   11/20         11/15         !                         !
                                                   !                         !
1971                                               !                         !
                                                   !                         !
1972     11/40           11/45       11/05  11/10  !                         !
           | \          /     \        |           !                         !
1973       |  \        |       |       |    11/35  !                         !
           |   \       |       |       |           !                         ! 
1974       |    \      |       |       |           !                         !
           |     |     |       |       |           !         LSI-11          !
1975       |     |     |     11/70     |           !     11/03     \         !
           |     |     |       |       |           !       |        |        !
1976       |     |   11/50   11/55   11/34         !       |     LSI-11/2    !
           |     |           /       11/04         !       |                 !
1977     11/60   |          /        11/34A        !       |                 !
                 \         /           |           !       |                 !
1978              \       /            |           !       |                 !    PDT-11
                   \     /             |           !       |                 !
1979                11/44              |           !     11/23               !
                                       |           !       |                 ! 
1980                                 11/24         !       |                 !
                                       |           !       |                 !
1981                                   |           !     11/23+              !
                                       |           !     /    \              !
1982                                   |           !    |      |             !
                                       |           !    |      |             !
1983                                   |           !    |      |             !
                                       |           !    |      |             !
1984                                   |           !  11/73    |             !    PRO350,325
                                       |           !    |      |             !
1985                                   |           !    |      |             !
                                       |           !    |      |             !
1986                                   |           !    |      |             !    PRO380
                                       |           !    |      |             ! 
1987                                   |           !    |    11/53           !
                                       |           !    |                    !
1988                                 11/84         !  11/83                  !
                                       |           !    |                    !  
1989                                   |           !    |                    !
                                       |           !    |                    !  
1990                                 11/94         !  11/93                  !

If you click on the numbers, you'll get a page about the respective -11, with some photos and a few words about its history and specs. I hope I can add more information soon: if you have anything to say about the -11 (specs, corrections, or a personal story) let me know! But please: don't ask me for part numbers, spare parts, questions like "how do I boot up the 11/24 I bought yesterday on eBay" or "how do I format a harddisk" in e-mail! I also don't sell systems or system parts. Thank you for not writing questions and request concerning such things!