VAX 780 on eBay

[Peter Corlett]

On Sun, Jan 02, 2022 at 06:59:47PM -0700, ben via cctalk wrote:
> On 2022-01-02 6:28 p.m., Zane Healy via cctalk wrote:
[...]
>> On that note a Raspberry Pi 2b running SIMH/VAX is about 1.6 VUPS.
> But can the Pi handle a gazillion students all time sharing at once @
> 2400? How long was the VAX timesharing era as I suspect networked PC's
> come out soon after that.

Probably about as well as the actual VAXen back when I was failing my
degree. I remember trying (IIRC) "SET PRI" once to lower my session priority
one notch, and while I did eventually get a DCL prompt back, it was
basically unusable. It was hardly a speed demon even at default priority,
and I returned to my Amiga to get anything useful done.

Raspberry Pis have between zero and six serial ports, depending on model,
amount of faffing about, and whether you consider three-wire LVTTL to be a
serial port or demand a full seven-wire RS232 port. Beyond that, you're
going to have to multiplex connections over some other port, with Ethernet
being by far the most obvious choice.

Meanwhile, back at the university in the mists of time, they had rooms full
of dumb terminals, mostly VT220s but some VT420s, connected to an X.25 PAD
which then winged its way to the VAX cluster, and indeed onwards to JANET,
so it's not "cheating" to multiplex over a packed-switched WAN connection on
the Pi. I expect the VAX's directly-connected serial port(s) would have been
reserved for the operator console.

The Pi 4 is between three and ten times faster than the Pi 2, depending on
task. I'd expect SIMH to fall towards the bottom of that range, but 5 VUPs
isn't to be sniffed at, especially as that is presumably a per-core
limitation and you could run a cluster of four of them. On a device which
draws ~7W at full tilt.