5 May
2021
5 May
'21
5:18 a.m.
On May 5, 2021, at 1:07 AM, Chuck Guzis via cctalk
<cctalk at classiccmp.org> wrote:
Very large machines, certainly. There were "site preparation" documents
that detail this.
I can quote from the 1975 edition of the STAR-100 hardware manual on
bitsavers (PDF page 25):
"Power for the basic computer consists of one 250 kva, 400 Hz motor
generator set. The motor-generator set has the capability of providing
power for the CPU, MCS, I/O and the MCU. The optional memory requires
the addition of an 80 kva motor-generator set."
Granted, the STAR was a monster of a machine, but similar setups were
used for CDC 6000, 7000 and Cyber 70, 170 machines and others. That
doesn't include the refrigeration necessary for the chilled water
supply. I/O devices such as card readers and tape drives often used a
"split" supply with the 400Hz supplying the electronics and normal 50/60
Hz AC supplying power for motors, etc.
That's definitely the case for the CDC 6000 series, the drawings make this clear. The
6600 mainframe takes 3 phase 400 Hz for power supplies, and 3 phase 50/60 Hz for the
compressor motors for the cooling system. Similarly, the DD60 console display for the
6000 machines takes 3 phase 400 Hz power for its power supplies, but single phase mains
power for some auxiliary functions.
An earlier message commented on the whine from power converters. I don't know how
common this practice was, but at the University of Illinois PLATO system which had a pair
of 6500 systems, the motor-generator was located near the elevator machinery in a corner
of the building, far from the computer room. Yes, it was noisy, but no one spent any time
in that location. The computer room was -- by mainframe standards certainly -- rather
quiet. Of course it helps to have liquid cooling, so there weren't many noisy fans to
deal with.
paul