MicroVAX II performance?

[Chuck Hedrick]

I just came back from DECUS.  One interesting talk was about implementing
Ultrix on new processors.  It reported the results of the first 2 of 4 such
projects that they are working on this year (the 8600 and the microVAX II --
when asked what the other two were, they just smiled).  In the Q & A, I
asked the question "What is likely to be the difference in performance
between a microVAX II and a 780?"  Here is roughly what he said.  (This is
from memory, by the way, and I don't claim to have an eidetic memory.  I am
integrating the answers to a couple of questions.)

We get asked this a lot.  The first thing we always try to make clear is A
MICROVAXII IS NOT A 780.  It is the greatest thing you would ever want to
see as a single-user system.  I've got one under my desk, and the day
somebody tries to take it, they'll do it over my dead body.  But we have
never claimed that it will do everything a 780 will do.  In fact in some
cases, it isn't even a 750.  It is not a matter of CPU speed.  The chip is a
real screamer.  But there are two critical differences between a microVAX
and a 780:

1) The microVAX II is a single-bus system.  We normally configure 780's with
more than one Unibus adapter.  We try to put bus hogs such as the UDA50 and
DEUNA on separate buses.

2) The combination of controller and disks simply do not have as much speed
as a UDA50 with an RA81.  We have played with a hypothetical controller
similar to the UDA50, and it seems to get about twice the throughput of even
a system with 2 RD53's.

[end of detailed summary]

The responder seemed to think that it would be unlikely that a microVAX, as
currently configured, would be able to support 16 users.  He implied that
with the KDA50 (the hypothetical Q-bus version of the UDA50), it would.
Obviously it is unfair to expect a single number for user capacity, since it
depends so much upon what is going on.  But it sounded to me like 8 might be
feasible.