MicroVAX I

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MicroVAX I
Announcement date: October 1983
FRS date: late 1984
Codename: Seahorse
OS support (VMS): MicroVMS V1.0 to VMS V5.0-2
OS support (ULTRIX): ULTRIX/VAX V1.0 to ULTRIX/VAX V2.4?
Enclosure(s): BA23
CPU Details
CPU module: KD32-AA
Number of processors: 1
Translation-buffer: 512 entries [1]
Cache: 8KB
Compatibility mode: No
Console processor: CPU
Console device: None
Minimum memory: 512KB
Maximum memory: 4MB
Q-bus: 1 @ 3.3MB/s
LAN support: optional

The MicroVAX I was the first of a number of MicroVAX models from DEC. It used the QBUS as its primary bus between the CPU (the KD32 CPU) and main memory, the only VAX to do so. It was said to be the slowest VAX ever (about 0.25 VUPs), even slower than the VAX-11/730 resp. VAX-11/725.

The two boards of the MicroVAX I CPU communicate over the CD interconnect of the H9278 backplane, and an over the top flat cable.

With a VCB01 Monochrome Video Subsystem added, the MicroVAX I becomes a VAXstation I.

Boot ROM

Boot ROM Restrictions

The MicroVAX I bootstrap ROM can only bootstrap a system disk attached to the first Mass Storage Control Protocol (MSCP) controller.

See the instructions from: AA-KM46A-TN MicroVMS 4.6 Installation and Operations, Chapter C.1 Creating a Console Diskette:

The console diskette will contain files used to bootstrap from a disk attached to the second MSCP controller. Use the following steps to create a console diskette. This example assumes that the first RC25 disk attached to the second MSCP controller (DABO) will be the new system disk:

  1. Log in to the system manager's account, SYSTEM.
  2. Check the first diskette drive to ensure that it is empty and inactive; the red diskette activity light should not be glowing. If there is a diskette in the drive, remove it following the instructions in Section 3.1.11.
  3. Label a scratch diskette CONSOLE DISKETTE. A scratch diskette is a new diskette or a diskette containing no information that you want to save.
  4. Enter the following command to invoke the command procedure that creates a console diskette for a MicroVAX I system:
What system disk do you want to be able to boot from? DABO
Ignore the informational messages displayed on your terminal screen. The procedure prompts you for the name of the diskette drive on which the intermediate media (console diskette) will be mounted. In this example, the media is mounted in diskette drive 1 (DUA1).
Where will the intermediate RX50 media be mounted? DUA1
Insert the diskette labeled CONSOLE DISKETTE into drive 1 and enter YES in response to the following prompt:
Are you ready? YES
When it has finished building the console diskette, the system displays the following message:
The media on DUA1 may now be used to boot device DABO

After you create the console diskette, write-protect it to prevent anyone from accidentally overwriting the contents. To write-protect a diskette, cover the square notch in the upper-right comer of the diskette with a silver tab. Note that in order to bootstrap the system, the console diskette must be in diskette drive 1.

You may want to add the following command to the end of SYS$MANAGER:SYSTARTUP.COM to mount the console diskette automatically every time you bootstrap the system. This prevents other users from removing the diskette thinking that the drive is not in use.



The command procedure SYS$UPDATE:VMBUVAX1.COM and other files needed might not be on the system disk depending on the option used when the system was installed.

You can install the missing components using:


The tape (resp. tape image) AQ-FP13D-BN_MICROVMS_4.6_87 must be loaded (resp. attached to) the TK50 tape drive beforehand.

Answer all questions with N:

* Do you want to install the entire kit: N
* Do you want to install the MAIL utility: N
* Do you want to install the SEARCH utility: N
* Do you want to install the DIFF utility: N
* Do you want to install the DUMP utility: N
* Do you want to install the RUNOFF utility: N
* Do you want to install the PHONE utility: N
* Do you want to install the MicroVMS HELP library: N
* Do you want to install the Remote terminal support via SET HOST/DTE: N
* Do you want to install the Foreign Terminal Support: N
* Do you want to install the LAT-11 terminal server support (via Ethernet): N
* Do you want to install the Stand-alone backup on system disk support: N

except for:

* Do you want to install the MicroVAX-I bootstrap that works for any MSCP system device: Y

You should now be able to set up the special boot diskette for booting from a disk attached to the second MSCP controller.

Supported Boot Devices

Boot ROM Characteristics

  • Microverify is the name given to the diagnostics executed by the MicroVAX I boot ROM. There are three LEDs on the DAP module and a seven segment display on the patch panel which will isolate the problem (if any) to one of the two CPU modules.
  • Floating Point Instructions in Microcode
  • No TOY Clock


There are a lot of MicroVAX I Options; some of them are not "officially supported", but work nevertheless.

Memory Options

The MicroVAX I uses standard Q-bus memories which are not as fast but are also less expensive and usable by both the MicroVAX I and other 16-bit processors (such as the MicroPDP-11). There are 22 address lines on the Q-bus, limiting maximum memory to 4 MB.

  • MSV11-P Parity Memory
  • MSV11-Q Parity Memory
  • MSV11-M Parity Memory: not supported and not yet tested, but supposed to work
  • MSV11-J PMI ECC Memory: not supported, but working! (-JD and -JE variants only; the -JB and -JC will not work)
  • MSV11-R PMI Parity Memory: not supported and not yet tested, but supposed to work

Mass Storage Options

The SIMH MicroVAX I supports the RLV12 controller for RL01 and RL02 removable disks.

It is currently unknown/untested whether the 'real' MicroVAX I supports the RLV12 controller as well.

Anyway, booting from an RL01/RL02 is not supported by the MicroVAX I boot ROM.

Communication Options

Video Options

  • VCB01 Monochrome Video Subsystem


MicroVAX I is the only MicroVAX model with "old-style" VAX Diagnostic Supervisor (VDS) diagnostics.


Sample MicroVAX I Boot Messages (MicroVMS V4.6)

These messages are taken from my 'real' MicroVAX I:



00000000 03

>>>B DUA0

  MicroVMS Version V4.6  6-Jul-1987 17:00


The MicroVMS system is now executing the system startup procedure.

The MicroVMS system is now executing the site-specific startup commands.

%RUN-S-PROC_ID, identification of created process is 00000015
%RUN-S-PROC_ID, identification of created process is 00000017
%SET-I-INTSET, login interactive limit = 64, current interactive value = 0
  SYSTEM       job terminated at 28-MAR-2022 08:30:57.94

MicroVMS V4.6

Username: SYSTEM

        Welcome to MicroVMS V4.6

    Last interactive login on Saturday,  3-DEC-2022 17:59
    Last non-interactive login on Monday,  3-JUN-2013 15:41

Main Menu

 1 - Exit to DCL
 2 - Log out of the SYSTEM account
 3 - Invoke the MAIL utility
 4 - Invoke the PHONE utility
 5 - Add a user account to the system
 6 - Install optional software
 7 - Add or Delete a MicroVMS component
 8 - Create or Modify an Autologin Terminal
 9 - Back up or Restore the user files on a disk
10 - Build a Standalone BACKUP kit
11 - Set the maximum number of interactive logins
12 - Configure the network
13 - Shut down or start up the network
14 - SHUT DOWN the system

Enter a number (? or ?# for HELP): 1

If you wish to use the menus again, type the following:



[1] MicroVAX Handbook. EB-25156-47
[2] Systems & Options Catalog. European Edition. Spring 1990.

External links