<Ibmekon> wrote:
> The thing most dreaded when I worked on an Ibm 370 was an uncontrolled
> power down.
> When the CEs finally arrived (my guess is they drew straws) - it
> seemed to take around half a day to reset all the trips ready for a
> normal IMPL load.
> At this stage, there would be open panels on the processor , control
> units , card reader etc.
Dumping power was certainly not a desirable way to treat the system, but I
don't recall ever needing CE assistance to bring the system back up. (We
never had an EPO pulled, but all that it took to restore the switch was a
small screwdriver.) In any case all that happened in the computer and
peripheral frames was that the main power relay dropped out.
That was how it worked: one of the wires in the 6-pin power control cable
(universally called, somewhat misleadingly, the "EPO cable") was +24V
supplied from the CPU through its EPO switch. Loss of that +24V at a
peripheral was the way that EPO was signaled.
In the past 45 years I've held two full-time, full-year IT jobs; in the
first one we didn't have any UPS capability (sadly, the power there wasn't
particularly stable, which led me to buy an obscenely expensive Dranitz
power line event recorder so that I could argue with the physical plant
klutzes), but at the second job we had 90 KVA of UPS, which I soon increased
to 190 KVA. Back in the 1980s the power in that area was also somewhat
unreliable, so the investment in UPS (a pair of Exide 2045s and an Exide
8100) was worth it.
However...one day Physical plant, without notifying my operations manager,
brought in a FS guy to work on the fire alarm - and the idjut managed to
trip the emergency UPS shutdown circuit. IIRC at the time we were using the
UPS capacity to support a top-end 4381 MP, three vaxen and one or two
uvaxen, the head end for a Sytek broadband async net, a couple of Wang OIS
systems, the modem pool and, I suspect, the operators' coffee pot.
KerCHUNK.
It's amazing how loud dead silence can be.
Joe