Wayne, the memory problems that you're describing are generally
symptomatic of loading problems on the memory bus.  The problem is that
the 128MB modules that you are currently using are probably single rank
modules - that is, they use a single bank of memory.  The 256MB and
512MB modules are probably dual rank devices.  That means that each
module effectively loads the address and command buses twice as heavily
as the single rank modules.  So, when you put two of those modules in a
system, you're effectively putting four times the load on the address
and command drivers from the chipset.  Most chipsets are OK with that,
but some are not.  Your systems are probably marginal...some of them can
drive the added load and some of them cannot.

There are a couple of things that you may be able to do to overcome
this.  If the BIOS allows you to adjust the voltage on your system, you
may want to bump it up to 3.4 volts.  If you can change the bus speed,
you might try to run the bus one step slower (that is, run PC133 at
PC100 or PC100 at PC66).  If the systems work in either of those cases,
then it is almost certainly a loading problem.

If you find that is the case, then you have a couple of options.  The
first is to see if your vendor can provide you with single rank memory
modules.  The other is to find out if your systems will support (and
your vendor can provide) dual rank memory modules with x16 memory
parts.  The second option cuts the number of parts on the module in
half, but I'm not sure if anybody makes SDRAM modules with x16 parts
anymore.

Good luck!

Drew Dunn
The NOSPIN Group

On Wed, 2004-03-24 at 11:24, Wayne Copeland wrote:
> All good advice and that is what we have been doing.  For the added
> memory we asked IBM and Kingston what we should buy and they told
> us, not us telling them.  We have had no problems with any mixture
> of the 128MB modules.  It's only when we move into more than one
> 256MB or the 512MB modules.  Again, starting with IBM part numbers
> we were sold what should work.  It works in some but not others.  I
> still have not heard back from IBM on this issue.  Thanks to all.

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