On 24 Apr 98 at 10:15, D A V wrote:

> i have a 486 that was pieced together from spare parts lying around.  it
> was given to me with no documentation.  running win3.1, and blah blah old
> stuff.
> It initially had 4 meg of memory, then another 4 meg was added.  The
> chips are different looking, one is staggered one is not.  I still am
> unsure how to tell if it is parity or non.  i wish to add more, possibly
> 16 meg, but how do i tell?  so far, since it's a 486 i'm assuming parity
> because of the age.  but looking on the chips themselves i see that it is
> 72 pin, and on one of them there are 16 (chips) and the other 12.   I had
> thought that parity would have an odd number of chips on the memory
> module, so now that makes these non-parity, my bios has a selection for
> parity error checking, though it is disabled....so what do you all think?

  "Divisible by three" is a better rule of thumb here than "odd".

  72-pin SIMMs are 4 bytes wide.  So one with 12 chips has three
chips per byte -- almost certainly two 4-bit-wide data chips and a
1-bit-wide parity chip.
  A 72-pin SIMM with 16 chips has four chips per byte.  Odds are
reasonably good that these represent a "two-sided" or "double
density" arrangement of two pairs of 4-bit-wide data chips -- no
parity.  [I would not normally expect such a SIMM to be 4MB, more
likely 2MB or 8MB.  It may be that it's an 8MB, but that your
motherboard doesn't support it and only sees half of it.]
  So at a reasonable guess, it sounds like you have
one SIMM with parity, and one without.  Disabled parity checking in
the BIOS is the right setting for this combination.

  "Singe density" SIMMs are in 1MB, 4MB and 16MB sizes.  You should
have not trouble adding a 16MB SIMM to a 486 that offers 72-pin
slots.

David G