RE: a salute to stability

Joe Barrera (joebar@MICROSOFT.com)
Sat, 12 Jul 1997 18:03:54 -0700


> From: Joseph R. Kiniry [SMTP:kiniry@cs.caltech.edu]
> mourning the fact that we can't somehow switch the machine over to a
> battery pack for twelve hours...

In the good old days when men were men and computers were computers
(with front panel switches and all), you could accomplish it if you were
reasonably quick:

http://www.cs.man.ac.uk/CCS/s100/s100home.htm

"Thus the S-100 bus provides most of the voltages likely to be needed by
chips, in the form of unregulated DC rails of nominally +8V, +/-16V. By
unregulated, I mean full-wave rectified and smoothed by a single
electrolytic filter capacitor (a huge 180,000F affair the size of a
baked-bean can, in the case of the main +8V power rail, which could
deliver getting on for 30 amps in some machines - enough for light
welding).

"A side-effect of the presence of this size of filter capacitor is that
enough charge is stored to let the system ride out mains dropouts
shorter than about half a second. I have often seen a Horizon or similar
machine sail blithely through a dropout that momentarily dims the room
lights, while modern PC/AT-clones in the same room reboot or hang."

Here's a picture of the inside of the IMSAI 8080 (the first computer I
used):

http://www.rdrop.com/~jimw/ims-2.jpg

Now THOSE are capacitors.

- Joe

Joseph S. Barrera III (joebar@microsoft.com)
http://research.microsoft.com/~joebar
Phone, Office: (415) 778-8227; Cellular: (415) 601-3719; Home: (415)
588-4801
The opinions expressed in this message are my own personal views and do
not reflect the official views of IMS Associates Inc.