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From: gwalker@SPCA.BBN.COM.UUCP
Newsgroups: mod.computers.vax
Subject: Re: VAX CPU SID's
Message-ID: <8703301908.AA01250@ucbvax.Berkeley.EDU>
Date: Mon, 30-Mar-87 11:31:53 EST
Article-I.D.: ucbvax.8703301908.AA01250
Posted: Mon Mar 30 11:31:53 1987
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In reply to the message from M. S. Pung at ornl-ncc.arpa (my mailer doesn't
recognize that host):

Every different VAX model has a slightly different format of the SID.  All
use bits 24-31 for a number identifying the VAX model. (31 is the highest
order bit). After that, bits 0-23 are used differently for different
models. For the 780, 782, 785, 8600 bits 0-11 are "The serial number
assigned to the CPU" and each of those models has 3 or 4 bits assigned to
"The number assigned to the Digital Equipment Corporation facility where
the CPU was manufactured". The quotes are from my VAX Hardware Handbook
which does not mention microvaxen or anything newer than the 8600.

For the 750, 725, 730 processors there are no bits allocated to either
of a machine serial number or a DEC facility. They have 3 fields each -
one for the software revision level of the CPU microcode, one for the
revision level of the CPU hardware, and one that isn't used. Not too
much opportunity for uniqueness there.

I haven't seen the handbook for microvaxen or the 8200, 8300, 8500 series
so I don't know how the bits are assigned for those. I'm told that it
is fairly likely to have 2 750's or 2 microvaxen with the same SID if
they were ordered at the same time and configured the same.

Probably what you are doing is safe enough if you are doing it for a limited
number of systems. One can't rely on the SID's to be completely unique
everywhere though as you can see from the above.

-- Gail