My mac G4 dual 800 has 2 512meg pc100 memory chips. I sometime have
what seem to be crashes due to memory failure. I notice (by looking in
System Profiler) that one of the chips is PC100-3225 and the other is
PC100-2225. What is the difference and could the mismatch be causing a
problem?

Howdy editdroid-ga,

Not so much a memory mismatch, but rather the wrong type of memory could
be your problem.  This OEMPCWorld article explains the differences between
the PC100-322(5) and PC100-222(5) DIMMs.
http://www.oempcworld.com/support/Apple_Firmware_Update.htm

"A PC100-322 DIMM can run at 10ns (100MHz) speed in CL3 mode ... and
it will typically run at 12ns (83MHz) or 15ns (66MHz) in CL2 mode. A
PC100-222 DIMM can run at 10ns (100MHz) speed in CL2 mode, but will
typically run at 8ns (125MHz) in CL3 mode."

The article goes on to say:

"Apple has always required PC100 RAM that is 8ns or faster. ... The ...
G4 require 10ns. PC100-222 RAM will only run at 8ns (125MHz) or faster
when in CL3 mode, in CL2 mode it will only run at 10ns (100MHz)."

So, the PC100-3225 DIMM in your machine might not be fast enough.

But, your system profiler might not be giving you a proper report.
From a MacRumors forum posting.
http://forums.macrumors.com/showthread.php?s=&threadid=68650

"Yeah, I think I've heard that SystemProfiler doesn't always report the
correct RAM speed."

You might take into account this Apple document announcing the Dual 800
MHz Power Mac G4.
http://www.apple.com/pr/library/2001/aug/20pmg4.html

"Housed in the new 'quicksilver' enclosure, the 800 MHz dual processor
Power Mac G4 includes:
...
- 256MB of PC133 SDRAM memory"

Even if you do not have one of the "quicksilver" G4s you might want to
run PC133 RAM on your machine, but you should probably open up your box
and check what you really have installed.

There is also a patch mentioned on the OEMPCWorld page that might take
care of the problem of misidentified RAM, but I would be cautious with
such things.
http://www.mactcp.org.nz/DIMMFirstAid.sit

"We are beginning to receive reports from testers who have used the fix,
and the reports are positive."

I would also go to the Apple web site and see if there are any patches
you should be applying as well.
http://www.apple.com/support/

If you need any clarification, feel free to ask.


Search Strategy:

Google search on: PC100 322 222
://www.google.com/search?q=PC100+322+222

Google search on: "System Profiler" incorrect memory
://www.google.com/search?q=%22System+Profiler%22+incorrect+memory

Looking Forward, denco-ga - Google Answers Researcher

That is not an answer; it's an education. thanks..

Greatly appreciate the 5 stars, kind comment and generous tip, editdroid-ga.

Was an educational process for me as well.  My pleasure!

Looking Forward, denco-ga - Google Answers Researcher