VAXstation 3100/76 SCSI disk over 1GB

Mike Cesari mcesari at
Fri Apr 22 00:14:50 CDT 2005

On Apr 21, 2005, at 10:12 PM, Saquinn624 at wrote:

> Dont know if this is common knowledge, but I have a VS3100/76 that I 
> threw a
> 2gig IBM drive in, tried to put VMS on and - it worked. All the stuff 
> I saw
> seemed to indicate that 3100s didn't like sysdisks over 1 gig, but my 
> /76
> doesn't seem to mind.
> There it is if it's useful
> Scott Quinn

This was at the time very annoying. We wanted to use what turned out
to be affected systems as boot nodes for LAN-based clusters and were
trying to use bigger disks. ("Damned disks work on Viking controllers
on the 3200's! WTF is wrong with these 3100's ?!?!?") Funny now... :-)

The actual problem was that "Early" MicroVAX 3100 and VaxStation 3100
boot ROMs use 6-byte SCSI READ and WRITE commands which limit access
to 1.06GB.

At some point VS3100-76's (and later) came fixed from the factory. I
don't remember when MicroVAX 3100's were fixed. I *think* DEC released
a fix for some models of MV3100's, but never for VS3100's.

VS4000's never had this problem.

To make life easier, a very unofficial fix was created and is still
available here:
There's a README and the patches are in


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