Computer system VAX/VMS







Anders Löfstrand

Datorhall In the mid 70's Digital Equipment Corporation (DEC) developed a computer system called VAX/VMS (Virtual Address eXtension / Virtual Memory System). It was based on the experience from the popular 16-bit PDP-11 that was built around the LSI-11 chipset from Western Digital.

VAX was one of the first commercial computers with 32-bit architecture. With VAX came the new operating system VMS. VAX and VMS were well designed and were made to work together.

First out in the VAX-family was VAX-11/780 released in 1977/78 followed by 750 and 730. Thereafter MicroVAX, VAXstation and all other models. Most products were well made but DEC personal computers were commercial failures.

VAX was a CISC-machine (Complex Instruction Set Computer) but in 1992 DEC introduced a RISC processor called Alpha. It was a fast 64-bit computer and could be run under OpenVMS or UNIX.

In 1998 Compaq acquired DEC and the VAX-era was over.

     Below is an example of a VAX-system in the mid 80's.

  • VAX-11/750, 14 MB (max), Floating Point FP750.
  • Expansion cabinetts: 2 Unibus, 1 Massbusadapter
  • Laboratory interface LPA11 (A/D/A-conversion)
  • DMA-controller DR11W and IEU11A (HP-IB)
  • Disks: 3 st. RA81 (3x456 MB)
  • Tape station TU78 (1600/6250 bpi)
  • Local Area Vax Cluster (LAVC) with VAXstations
  • Communication: DECnet och PSI Mail (Datapak X.25), Kermit
  • System printer: Printronix P600
  • Standard terminal: Tandberg TDV 2230 (graphics for Tektronix 4010/4014)
  • Computer graphic: UNIRAS

     And a CI-cluster in the early 90's.
  • CI: HSC-50
  • VAX 8550, 64 MB, CPU- and expansion cabinet.
  • Console: PC38N (PC under special O/S)
  • DMA-controller DRB32
  • Ethernet interface: DEBNA
  • Disks: SI91 (606 MB), SI95 (1.7 GB), SI 817 (1.7 GB). In all 16 disks/15 GB
  • Tape station (CI-interface): TA81 and TA90E with data compression (IDRC)
  • Editors: EDT, EMACS
  • Compilers: Ada, Basic, C, Fortran, Lisp, Pascal and Simula.
  • Math library: NAG (Fortran subroutines)
  • LAN: FDDI Backbone 100 Mbit/s. Ethernet 10 Mb/s (802.3).


Due to better price/performance we had at this time moved to acquire disks from
System Industries, as you can see in the table.

And for economical and technical reasons we moved from proprietary to more open
systems and due to the fast changes on the computer market even to leasing of

VAX/VMS was famous for its almost mythical stability and according to a rumour the
Irish railway had one VAX-system that worked 18 years without reboot. Not bad.

The Cheshire cat is DECUS VAX SIG's mascot. The cat is a character in the book Alice in Wonderland, by Lewis Carroll. Charles Dodgson, better known by his pen name, Lewis Carroll, was an English writer and mathematician in the nineteenth century.