Where to get a Vax or microvax

tony duell ard at p850ug1.demon.co.uk
Mon Jun 29 11:08:06 CDT 2015

> on real hardware. What would be the best machine for a beginner to VAX
> Hardware to start out with?

I think you need to think very carefully about what you want this machine to do. 
The ideal VAX for me is not going to necessarily be the ideal VAX for you.

In general there are 3 classes of VAX that people run at home. There are many
other families, but in general they are much rarer, and probably much harder to 

The first series are the VAXstations, probably a 3100 of some kind. These are 
desktop boxes, they are workstations (so you can drive a CRT monitor from them,
although they have serial ports too, and AFAIK can use a serial console). They
generally have SCSI and ethernet interfaces built in. The downside is that they
are somewhat closed machines. You have connectors for a memory board in
most of them. You have the SCSI bus for disks. But you don't really have access to
the CPU bus to add anything out of the ordinary. This may well not matter to you.

The second series are the MicroVAX II/III machines. Normally in a deskside-size
cabinet. Normally use a serial terminal, but there are exceptions. Here the CPU is
one board, memory is one or 2 more, then separate boards plugging into something
called Qbus for everything else. The advantage, of course, is that Qbus is the processor
bus so if you need a strange interface you can probably add it. The disadvantage is that
finding some of the boards you may want is a pain (Qbus SCSI is often hard to get)

The third series I hesitate to mention, as I don't think they're what you are looking for. That's
the first ever VAX series, the 11/7xx machines. There are 3 sub-families. The 11/780 was the first
It's massive (think large wardrobe just for the CPU) and needs 3 phase mains officially. The 
upside for a hardware person is that said CPU is massive because it's built from lots of simple,
standard, ICs. It's repairable. Very. The 11/750 came next, a bit smaller, but now the CPU is
a lot of custom gate array chips. One that I would avoid (yes, I know I'll get flamed for that from
all the happy owners). To me the 11/750 is large and doesn't give you anything over a microVAX
The third subseries is the 11/730. It's slow. It's very slow. I am told that using the DEC supplied
microcode tape it can take 25 minutes to get a boot prompt (!). But it's small, the CPU is one
10.5" high, 19" wide rack mount box. A useable machine fits in a half-height rack. And amazingly
this small VAX was built from standard ICs (admittedly a lot of PALs), mostlly. These machines use
an expansion bus called Unibus (the 11/780 and 11/750 also have MassBus for disks). Unibus is 
similar in concept to Qbus, so again you would have a board for ethernet, one for serial terminals,

For me, a hardware hacker with too many machines as it is, the 11/730 fits the bill. I can accomodate
it (I doubt I could fit an 11/780 in anywhere) and I can hang a logic analyser off it if I want to. For you,
I think you should probably look towards a VAXstation to start with. But I might be very wrong...


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