VAX 11/750 info

From: Ethan Dicks <ethan_dicks_at_yahoo.com>
Date: Fri Jul 27 16:57:37 2001

--- Bill Bradford <mrbill_at_mrbill.net> wrote:
> Anybody know what the power requirements for an 11/750 (base
> unit) are? I've got a chance to get two of them for cost of
> freight...

I don't have one in front of me, but ISTR that just the CPU with a full
boat of RAM, not including any external BA-11s, disks, etc, pulls between
8-12A _at_ 110VAC. The mains is a 30A Twist-n-Lok connector, in case you don't
have one already wired-in at home (I do! ;-) I wouldn't be surprised if
half the power went to the blower.

Filling the internal Unibus would, of course, raise the bar somewhat, at about
50-100W per board, I think.

Nice machines. If you are lucky, they've been upgraded to take 14Mb of
RAM. I only have 8Mb in mine. :-( It originally shipped with 512Kb
and I did the upgrade myself when my employer used to own it (extra backplane
wires, flip some switches on the CPU ID DIP pack (another post-factory
upgrade!) and replace the mem controller).

I think they are a good compromise between size and speed if you need PDP-11
compatibility mode. The 11/730 has a "real" console (the 11/750 runs out
of its own ROM; it does not have a micro as a console processor and,
therefore, does not require console media to start up (but there was a
microcode patch late in life that may or may not be needed before the OS
boots up, so some 11/750s *did* have a start-up TU-58)), but is about 50%
as fast as an 11/750. Everything larger than an 11/750 is faster, but
harder to move and sucks more power.

If you are going to run one of them on a regular basis, you might want to
check first, to see what boot ROMs are on it, since unlike the 11/730 and
11/780, does have them. Really old 11/750s might not have an MSCP boot.
Ours did not (it shipped with RK07sand was originally fitted with a Systems
Industries SI9900 SMD controller; it didn't see an RA81 until it was six or
seven years old).

The other thing to see is what MASSBUS cards are in it. You might find
just a MASSBUS card for disk and tape (we had RM02s (for emergency purposes)
and a TU78), an SI 9900 card (2 x 40-pin Berg connectors on the I/O panel),
or even a second Unibus controller (DWBUA). We always had all the MASSBUS
slots populated, it just depended on what year it was as to what was where.
A 32-bit path to disk was great back in those days.

-ethan


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Received on Fri Jul 27 2001 - 16:57:37 BST

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