On 10/15/07, Tony Duell <ard at p850ug1.demon.co.uk> wrote:
So you want me to start off with a VAX?
Lots of folks on this list have lots of nice things to say about the 11/750.
Personally, I theink the 11/750 is not the best machine to try to keep
running. The reason is that the CPU is made up of a large-ish number of
custom gate array chips. Even when they were available as spares from DEC
they were very expensive, now they're unobtainanle other than by raiding
other 750s.
I agree that the custom gate arrays make the 11/750 unrepairable
(except for raiding parts), but I still think it's a good compromise
between size and performance, for the VAX-11 line.
If you have the space (and it's large), try to get
am 11/780. I've never
been inside one, but I've read the printset (schematics) and it seems to
be all standard chips.
Yes.... repairable, but large and power hungry, and, IMO, more
difficult to obtain than an 11/750 (partially due to quantities sold,
but also due to how long ago 11/780s were turned off and sold/scrapped
compared to 11/750s). Neither are _easy_ to find, but I think it's
more likely to find a dusty 11/750 in a corner of a warehouse than an
11/780.
If you don't have the spave, and can stand the
lack of speed, consider an
11/730. It's small (1 10.5" high rackmount unit), you can fit the
processor, disk and tape drives into a half-height rack (this was a
standard configuration). It's almost all standard chips, 2901 ALUs, TTL,
non-protected PALs, etc.
Yes. There were two system packages - the older 11/730-Z box
(10.5"-tall rackmount box in the middle of a 42" rack, with room for
an RB80 below, and an RL02 above), and a newer BA-11-style package
(don't know the designation), with the CPU chassis up top and hidden
behind a full-height door (also 42" rack), and room for cable
management below. The 11/730-Z is a self-contained system, with (as
shipped) a 121MB fixed "IDE" disk (in the sense that the disk
controller is a special board and "integrated" into the CPU in a
special slot - it's a simplified SMD interface to the drive, IIRC) and
10MB removable (known as DQA0: and DQA1: in VMS), room for up to 5MB
of memory, a DMF32 serial/printer interface (8 async, 1 sync, one
parallel out that can be used to drive a line printer), and a couple
empty slots.
The 11/725 is also a nice package if you can find one - same CPU cage
as the 11/730-Z, but supposedly only rated to 3MB (I heard that some
backplanes had 2 memory slots filled with epoxy, but never observed
one). It's in a smaller, roll-around-pedestal "office friendly"
package, with an RC25 drive mounted standard (but you aren't limited
to it). There have been numerous threads on the RC25, but suffice it
to say that you may find it difficult to find a working one after this
many years.
You can put 3rd party controllers, like SMD or SCSI in either the
11/730 or 11/725, or you can hang an external BA-11 off of one and do
what you like (though the 11/730-Z makes it easy to route the BA-11
cable, and the 11/725 does not).
I used to have an 11/730-Z, but I had to leave it behind in a
downsizing 13 years ago. I do still have an 11/725, but have not
powered it up in many years.
I have seen VMS 5.0 running on an 11/725, booting off of RC25, even,
but VMS 4.x runs very well on them. It's hard to get much newer than
VMS 5.0 with only 5MB of physical memory. The CPU is slow enough that
I'm not sure I'd want to try something newer, even if it had 8MB.
There's a lot to be said for the old Unibus VAXen, as long as speed
isn't your goal. OTOH, unless you have prior experience with them or
have a Unibus board that you want to run (as I do), you might find a
MicroVAX of some flavor easier to find and easier to work with (but
probably not as easy to repair).
-ethan