Virtual Address eXtended or VAX was DEC first 32-bit computer. It was originally meant to be a simply a 32-bit virtual memory extension of the PDP-11. What it became was a new subclass of computers called super-minicomputers. Like the PDP-11 it uses either the Unibus/Massbus or Q-Bus. Some also use SCSI. Some of the high end machines use buses called VAXBI, XMI, and CI. VAXen (The plural form is up to debate, but most enthusiasts use “VAXen”) run either VMS or Virtual Memory System, an operating system that is still around today running on the x86, and ULTRIX (known both as ULTRIX-32 and VAX/ULTRIX), a proprietary UNIX. Some also run third party UNIX or BSD. Some also run a real-time OS called VAXeln. VAXen were originally networked using a protocol called DECnet but later models supported TCP/IP. There are a few different product lines of VAXen. A simple rule of thumb is that the MicroVAXen, VAXstations, and the VAX 4000 and 6000 lines use microprocessors. The following is a rough diagram of the different lines of VAXen.
VAX-11 — The original VAX line. It is backwards compatible to PDP-11 RSX-11. Unibus
VAXstation — The line of VAX workstation. Most have corresponding MicroVAX models.
VAX 4000 — The line that replaced the MicroVAX. Q-Bus
VAX 9000 — A mainframe line of VAXen. VAXBI and XMI
MicroVAX — The original microprocessor line of VAXen. Q-bus or SCSI
VAX 8000 — A high end line of VAXen replacing the VAX-11. Unibus
VAX 6000 — A mid-range VAX line. Some had multiprocessing. VAXBI
VAX 7000/10000 — The final high-end VAXen Had multiprocessing.