Beowulf - Single Board Computers? (long)

[Bob Drzyzgula]

On Mon, Sep 21, 1998 at 01:49:37PM -0400, Walter B. Ligon III wrote:
> --------
> 
> 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.

Well, yes. However, the ATX power supply harnass is fairly
complex as these things go. I believe that it requires at
many as six voltages (+/-5V, +/-12V 3.3V and +5V standby).
The 3.3V is optional but probably required if you're
using 3.3V SDRAM. The standby (several hundred mA)  has
to be delivered in advance of the power-up, I believe,
unless you disable the soft power on/off somehow, so you
have to wire it up separate from the regular +5V feed.
The power supply isn't supposed to deliver power other
than the 5V standby unless it gets the PW_ON signal from
the motherboard, so you need some sort of per-motherboard
logic control on the power feed lines.

I didn't intend to say that one *couldn't* do this, only
that it was hard compared to running 5V & 3.3V into a
four-pin Molex.

CEDIS may have found a simpler way to do this... does
anyone know for sure?

> ...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.

Yes, this is very true. However, what would be the cost
advantage over SBCs? Notebooks also lag desktops in
performance technology, and are also quite expensive. At
the same time, their product life cycles are brutal, so
you'd prbobably spend the rest of your life redesigning
the harnass for each new notebook, usually without benefit
of good documentation.

> 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?

This is correct if, as you say, one is using non-PC SBCs.
However most Industrial Computers are fully compatible
AT-architecture-looking things, and will run everything
from DOS 3.3 to NT 5.0 to Linux to OS/2 and Netware.
Even STD BUS looks pretty much like ISA, and STD-32
kinda looks like EISA. VME boards can be run without
recognizing the VME interface, and there may be VME
drivers for Linux, does anyone know? A minority of the
low-end X86-architecture machines, such as those made by
Micro/Sys, JK Microsystems and Tern don't seem to have a
standard BIOS or all the expected peripherals, and probably
can't run Linux.  But I run Linux on Jump SuperMOPSpro and
MOPS LCD 3 PC-104 boards with no trouble whatsoever. (Well,
perhaps the LCD 3, an ALi 386SX clone with 6MB of memory,
is a tad sluggish :-)

Cheers,
--Bob

-- 
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Bob Drzyzgula                             It's not a problem
bob@drzyzgula.org                until something bad happens
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