Mailinglist Archive: opensuse (1777 mails)

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Re: [opensuse] Moving to IPv6
  • From: Anton Aylward <anton.aylward@xxxxxxxxxx>
  • Date: Tue, 14 Sep 2010 12:42:00 -0400
  • Message-id: <4C8FA5D8.9010909@xxxxxxxxxx>
James Knott said the following on 09/14/2010 11:59 AM:
Anton Aylward wrote:
It used to that each rack had a PSU (for some stupid reason they always
seemed to be at the bottom) that delivered DC (+/-12V, ±5V) on busbars
to items in the racks.

That "stupid reason" would be weight. Power supplies have, until
recently, been very heavy. Putting them at the top would make the
cabinets top heavy. Placing the P.S. at the bottom also keeps AC power
away from the equipment. When you run AC power in a cabinet, you have
to be a lot more careful than you would with signal or DC power cables.

For every good reason there's a stupid example and for every good
reasons there's a good example.

My stupid examples from the DEC worlds of the 70s and early 80s (PDP-11
and VAX) where the cabinets had the PSU at the bottom include

... someone tweaking one of the boards and dropping a small tool into
the grill on the PSU. Trying - stupidly - to fish it out with a piece
of wire shorted the PSU - explosively. Five volts at mucho amps will
vaporise things like screwdrivers and Allen wrenches.

... leaving the cabinet's back door open and disturbing the heat flow,
and causing a fire because of the cardboard box of printer paper on the
floor next to the hot PSU holding the door open.

Yes, "stupidity". The Number one cause of incidents and accidents.

I don't know about heavy, though. Back in the mid 70s I needed a 50W
PSU for a piece of avionics I was working on. I pulled the catalogues
and built a custom switched mode PSU that fitted in one of those
kitchen-size matchboxes[1]. The toroidal transformer - OTS - was about
as big as my thumb. The 'trick' was running it at high frequency.
Which made smoothing easier as well. The case - doubled as the
heat-sink - was the heaviest component.

We are all agreed that your theory is crazy. The question which
divides us is whether it is crazy enough to have a chance of
being correct. My own feeling is that it is not crazy enough.
-- Niels Bohr
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