On 15 Aug 99, at 10:53, Larry Atlow wrote:

> I'm having a problem that's new to me.  A motherboard that doesn't
> recognize or report memory modules at their correct size.  I added two
> new 16MB (4x32) FPM, 60NS to a system which already had a pair.  At that
> point, the system reported 32MB at POST.  Pulling out one of the new
> SIMMs yielded 40MB instead of 48.  Pulling the existing SIMMs and
> installing just the new ones yielded 32.  Adding one of the old ones
> gave me 40 instead of 48 again.  Installing the second original SIMM in
> the fourth slot again put me back up to 48MB.  Individually, all of the
> chips test okay.  In matched pairs, they test okay.  I'm not aware of
> any CMOS settings that should affect how the memory is recognized.  Is
> it a SIMM compatibility problem, bad memory slot(s), a possible jumper
> setting, or something else?  Unfortunately, I don't have the manual for
> the system.  Any assistance greatly appreciated.
>
> MOTHERBOARD SPECS:
> OEM: GemLight
> Chipset: SiS-496-497/A/B
> BIOS: Award v4.50PG
> BIOS Version: 40-0205-2A4IBG39-V2.05

> Processor: AMD Am5x86-P75-133

  This is kinda important -- it's a 486-class CPU, so it should be able to
use 72-pin SIMMs singly rather than requiring them in pairs as a Pentium
would.  [AMD used "5x86" as the name for some of their advanced 486 models,
such as those with a 4x multiplier (which is how you get to 133 MHz); at one
point, they rated their 4x33=133 MHz part as roughly similar performance to
Intel's 75 MHz Pentium, hence the "P75" performance rating.]

  Briefly, you have four 16MB SIMMs; each is recognized as 16 MB in the first
two slots, but only seen as 8MB in either of the second pair of SIMM slots.

Diagnosis:

  It's not the RAM -- each SIMM works fin in the first two slots.

  It's not a configuration problem I recognize.

  It's not *just* a bad slot, since it appears to be a problem with both of
the second pair of slots.  My guess would be either a problem with the RAM
controller, or possibly a problem with the third slot AND a RAM controller
rule which says slot 4 cannot exceed (or must match) slot 3.
  I know of no practical repair for such a fault.  [There are those who would
argue that more than 32MB on a 486 system is wasteful....]  So I recommend
either (a) live with it, or (b) invest about $100 (maybe less!) in an upgrade
to a Socket 7 motherboard and Pentium-type CPU -- unless you insist on
"latest and greatest", your 64MB of RAM will still be usable.


David G

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