Beowulf - Single Board Computers? (long)

[Walter B. Ligon III]

--------

> > They may be
> > cheap, but traditional motherboards take up a bunch of
> > space for stuff that is little or no use in a Beowulf;
> > having to run 110VAC to each processor is kind of a
> > drag,
> 
> I'm not sure that AltaTech's commodity motherboard gizmo actually uses
> that many power supplies. The thing which makes it big is the disk and
> the ability to plug in a PCI card. Presumably if you had a motherboard
> with no disk and didn't need any cards because you were using built-in
> ethernet, you could get them to space the shelves closer than usual,
> giving you about double their current density of 32 systems per rack.
> 
> And it would be cheap. And it's only twice as big as your idea system.
> 
> Being as naieve about power as I am, would this beast use considerably
> less power if you had a consolidated gizmo for dishing out DC to each
> motherboard? My existing alphas with their 300? or 400? watt power
> supplies actually pull only 1 amp of 110V with just the cpu in use and
> 2 amps when they are using their disk drives. We measured this at the
> breaker box using one of those induction gizmos. If getting rid of the
> separate power supplies and not having a disk gets us down to 0.5 amps
> per CPU, we're getting close to your ideal number with commodity
> parts.
> 
> -- greg

The CESDIS Beowulf group built their current machine (ecgtheow) from
dual PII motherboards with built-in SCSI and 100baseT.  You do NOT need to run
110VAC to each motherboard, you run +/-5 and +/-12 (or something like that.
One could easily design a power supply to operate N motherboards.  People
have been designing powersupplies for years.

So you CAN make even standard motherboards fairly compact.  Also, you COULD
do the laptop motherboard trick and use the PCMCIA slot to run your network
card.  Removed from the case they wold be quite small and the power 
requirements
are simple DC.

As for "extra stuff" the biggest problem with using a non-PC based SBC is that
Linux would not run on it directly - it would need porting.  In the long run
you would probably want VxWorks or Qnix or something.  At that point we aren't
really talking about Beowulf, are we?

Walt
-- 
Dr. Walter B. Ligon III
Associate Professor
ECE Department
Clemson University