Re: Mersenne: Poaching (was Mersenne Digest V1 #573)

1999-06-14 Thread David L. Nicol

lrwiman wrote:

 *never ever* cheap out on power supplies. 

This is good advice, but personally I have never seen the
point of giving every machine in a rack of computers its own
power supply rather than having one big one and just running
DC all the way up the rack.  The fact that it is not done
that way seems to be about politics of having AC wall current
rather than engineering efficiency. 

Why not have a single (redundant) big 24VDC power supply for
all the boards instead of supplying them all 120VAC?


Would there be a commercial market for such "unicluster"
devices, where multiple independent boards are associated
with a single power supply transformer --- or maybe an alternate
power standard connector which would provide computer voltages
to computer equipment instead of 120 VAC?

Or is the current state of distributed power supplying really
a best practice because it prevents loading problems and
line resistance problems that running DC lines around the computer
room (using Edison wiring rather than a Tesla wiring) would cause?

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Re: Mersenne: Poaching (was Mersenne Digest V1 #573)

1999-06-11 Thread lrwiman

 A) A doublechecking cleanup team of computers. A team of (say) five
 PIII-500s, 64MB SRAM and suitable motherboards, with cheap everything else
 (cases, etc, and probably only one old monitor to share among them all)

As a computer repairman, of two years, I agree with my father of (5 years
computer repair experience, ~20 years electronics experience), and his 
co-worker (30 years of computer repair experience) that your *never ever* 
cheap out on power supplies.  And crappy cases almost always come with 
crappy power supplies.  This is expecially true for a team like that one
that would have to have constant operation. 

Crappy power supplies can cause flaky performance in innumerable ways 
relating to CPU and motherboard operation, as well as drive operation.

Just in case these things get built, what OS should they have, or does 
it matter significantly for speed?

-Lucas Wiman 
 

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Re: Mersenne: Poaching (was Mersenne Digest V1 #573)

1999-06-11 Thread Chris Nash

 co-worker (30 years of computer repair experience) that your *never ever*
 cheap out on power supplies.  And crappy cases almost always come with
 crappy power supplies.  This is expecially true for a team like that one
 that would have to have constant operation.
 Crappy power supplies can cause flaky performance in innumerable ways
 relating to CPU and motherboard operation, as well as drive operation.

I have to back Lucas up on this one, and can't stress it enough. In one form
or another over the past few years I've been involved in mathematical
computing 24 hours a day, seven days a week. Apart from one of the first
Gateway P-120 motherboards (which apparently had a known tendency to
overheat and Gateway were aware of it), an early US Robotics 28.8 modem
(which was lousy design) and a modem which was struck by lightning (forgot
to unplug the phone cord), the only hardware component to have failed has
been power supplies. I'm currently on my fourth power supply in 2 years on
my current machine.

When the power supply fails, I have been fortunate and not had any permanent
damage to other hardware components, mainly because voltage regulators tend
to be quite robust components and, even in a failure, don't let much more
than 3.3V or 5.0V hit the board. (Though exploding capacitors in the power
supply *will* blank the CMOS). However a power supply is notoriously full of
very poor, very cheap components. It is the 10c resistor, or 50c smoothing
capacitor that fails - not very comforting when you may have thousands of
dollars of hardware hanging off it. People who drive sports cars don't use
the cheapest gasoline...

It seems lately though that component quality is decreasing. AT power
supplies seemed pretty indestructable, but ATX power supplies are much
weaker. John Pierce is right, a $59 case isn't bad - I could have got the
latest power supply without a case for $48. Resist the temptation though to
go to a high street store and pick up a cheap power supply for $30... and
believe me, a spare power supply you have hanging around, or a reconditioned
one is *not* an option.

It's not worth spoiling the ship for a ha-penny of tar... if you're building
a decent system, don't try to save a few bucks on a power supply. A good
brain is useless if the heart stops. I'm reminded of the Russian guy in
"Armageddon" - "American components, Russian components... all made in
Taiwan!".

Chris Nash
Lexington KY
UNITED STATES
===
Co-discoverer of probably the 8th and 11th largest known primes.



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