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A MicroVAX II with an RX50 dual floppy drive
Announcement date: 14 May 1985
FRS date: May 1985
Codename: Mayflower
OS support (VMS): MicroVMS V4.1M
Enclosure(s): BA23, BA123, H9642
CPU Details
CPU name (VMS): KA630
CPU name (console): KA630
CPU module: KA630
Module: M7606 [1]
Number of processors: 1
SID: 08000000
XSID: 01010000
CPU chip: 78032
CPU technology: ZMOS
CPU cycle time: 200ns [2]
Instruction-buffer: 8 bytes [2]
Translation-buffer: 8 entries [2]
Cache: None [2]
Compatibility mode: No
Console processor: CPU
Console device: RX50 or TK50
Minimum memory: 1MB [1]
Maximum memory: 16MB [3]
Memory checking: Parity
On-board memory: 1MB [1]
Q-bus: 1 @ 3.3MB/s [3]
LAN support: optional [3]

The MicroVAX II was a small VAX, with the KA630 CPU‎‎ for its CPU. Its bus between the CPU and main memory was a special bus carried on over the back connectors as well as the CD interconnect of the QBUS backplane; it used the QBUS for its I/O bus.

The M7609-AP was a main memory board for it.

Operating Systems

The following operating systems can run on the MicroVAX II:

MicroVMS / VMS

In version 4 of the VMS operating system there were two different subversions:

  • MicroVMS - for the series of MicroVAX computers
  • VMS - for all other VAX computers

Both versions differ in contents and packaging:

  • MicroVMS software was distributed as set of numerous RX50 diskettes or on TK50 tape cassettes.
  • VMS software was available on standard 9-track magnetic tape or on removable disks, e.g. RL02 or RA60.

From version V5.0 onwards there was no more special version for the series of MicroVAX computers.

MicroVMS Support for MicroVAX II Computers

MicroVMS V4.1 was the first version to support the MicroVAX II computer.

VMS Support for MicroVAX II Computers

Some of the 'full size' VMS V4.x versions include MicroVAX II support, too, see the following table for details:

VMS V4.x Support for MicroVAX computers
Version Type Date MicroVAX Support Save Set Info
V4.0 Full 23-SEP-1984 NO ---
V4.1 Update 11-JAN-1985 YES VMS041.A: VMS041 / VMS041.B: VMS only / VMS041.C: MicroVMS only
V4.2 Full 12-JUL-1985 NO ---
V4.3 Update 9-JAN-1986 YES VMS043.A: Common Files / VMS043.B: VMS only / VMS043.C: MicroVMS only
V4.4 Full 30-MAR-1986 YES Integral part of all Save Sets
V4.5 Update 26-SEP-1986 YES Same as with V4.3 (individual Save Sets)
V4.6 Full 15-JUN-1987 YES Same as with V4.4 (integral part of all Save Sets)
V4.7 Update 29-OCT-1987 YES Same as with V4.3 (individual Save Sets)


Many UNIX variants were available for the MicroVAX II.

Digital Unix




Version 1.2 and higher of the VAX port of NetBSD can run on a MicroVAX II. I've even built some instructions using SIMH on how to do so, that may be adapted to a real MicroVAX but I don't have one to test with.


OpenBSD can run on the MicroVAX II as well, later versions are better for timing issues... 4.4 is the current good version.


The MicroVAX II is emulated in SIMH.


[1] MicroVAX II 630QY, 630QZ Technical Manual. AZ-FE06A-TN
[2] "CVAX-based Systems", Digital Technical Journal, Vol 1 No 7, August 1988.
[3] MicroVAX Systems Handbook 1988. EB-30991-41
[4] VAX Systems Hardware Handbook -- VAXBI Systems. EB-31692-46

External links