[HARDWARE] A load of motherboards: progress to date.

NP np at cableinet.co.uk
Tue Jun 30 23:32:58 EDT 1998


A couple of months ago I posted my proposed plan to stick a load of
motherboards in a box.
There seemed to be some interest, so here's an update.

I decided that a whole load of 486's was only going to be as good as a
couple of Pentium-II's and probably not worth the effort.  So, I decided
to go for Cyrix M2 200MHz chips (@233MHz) (good value I think).
The idea was to keep the boards pretty well bare; CPU, fan, 8MB RAM,
slim network card with EPROM boot chip, and to run multiple boards from
a small number of large power supplies.

Booting without video cards, despite positive information from
BIOS manufactures, turned out to be problematic, like the few boards
I tried to boot, would NOT, despite setting the BIOS to "Halt on NO
errors" (or whatever).  They wouldn't play.  The solution was to employ
TX PRO boards with on-board video (and sound, although surplus to
requirement) (again, good value I think).  Obviously these work fine
without video cards plugged in.  The on-board video insisting on taking
a minimum of 1MB of the available 8MB RAM is a little annoying, but it
works.

I chose to use Linux to get good networking facilites with good use of
minimal RAM.  (And it's my preferred o/s in general anyway).

The power supply idea was a bit iffy / risky.  I knocked up a couple of
chocolate block connectors on a block of wood, put this in-line between
the PSU and the m/b, inserting an ameter in-line with each rail in turn,
booting and measuring the current.  The total came to 265mA (not
including the CPU fan which is generally about 60 - 80mA); not much at
all.   The next step was to T off a parallel output from this hi-tech
block of wood and try running 2 m/b's.  The result ?  - it works, no
problems.  Current wise, I reckon a 375W PSU *should* probably run about
6 boards but I think I'll keep that number down to 4 to be safe (time
will tell).  As the CPU fans don't require a fancy PC PSU, I'll run them
independantly off some other simple 12V DC supply (possibly have 2
supplies running, with the in-use one holding relay contacts to one
side, making the connection to the fans.  If the primary supply fails,
the contacts will swing to the other [default] position and supply the
fans from the secondary supply - maybe overkill but I like the idea).
NetBoot for Linux was used to produce 16KB boot images for the EPROMS
(certainly didn't want the hassle of power / heat / space / cost with
loads of hard drives).  I now have 3 boards succesfully booting kernel
images from a server and mounting their file systems via NFS.
The next stage is to cable up the PSU arrangements, then throw in a few
more units.

The final stage will perhaps be to run a few LED / LCD display gadgets
off some parallel ports, (just for a bit of fun), for stats, messages,
and most importantly; impressive flashing lights.

And so far there has been only 1 small whiff of smoke !  This occurred
when a second hand PSU bailed out due to the complete lack of a fan (if
only I'd noticed that beforehand - no wonder it was quiet !).

Not quite FPGA technology but that's the toy so far.

Comments ?


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