SUMMARY - Mixing sun and non-sun memory on IPX

From: Dave Plummer (
Date: Sat Sep 28 1991 - 06:16:46 CDT

My initial message was as follows:

>>From SunFLASH Vol 33 #25
>>16MB and 4MB SIMMs can be used together in the same SPARCstation IPX as
>>long as it's Sun memory that is being used. Any combination of Sun and
>>non-Sun memory is not supported and is likely to cause parity errors.

> I recently replaced one of the 4Mb SIMMs in an IPX with a non-Sun
> 16Mb. All has been well so far. Can anyone cast light on the above
> announcement and indicate if there is any basis to the assertion, or
> could this be marketing disinformation?

The answer appears to be that the IPX, and indeeed the SS2, place a tighter
spec on memory than previous systems. Thus not ALL third party memory will

Several people reported success with third party memory in these machines
and no one has yet called in with reports of real failure,

I would advise those buying third memory for any system to specify the exact
machine on their purchase order so that the vendor is forced to accept some
responsibility for the suitability of the product.

A number of people pointed out that Sun could not be expected to 'support'
third party memory. Naturally the only level of support I would expect for
such items is that a defined hardware interface is presented.

Thanks to all those who replied

Tim Smith gave the fullest description of the requirements for these systems.
Thanks to:


Tim G Smith wrote

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Be careful where you get memory for SS2s (and IPXs). The timing
tolerances for the SS2 memory are very tight. In fact they are so
tight that there are only a couple of vendors who build memory that
meets the tolerances.

The critical specs are CAS precharge time (tCP = 10ns) and access time
from CAS precharge (tCPA = 45ns). Most vendors build chips with tCP
in the 12-15ns range.

If you buy memory that doesn't meet the specs you will get parity
errors. A parity error in user space will result in the process being
killed. A parity error in kernel space will cause a panic.

Make sure you get memory that meets the specs.

Sun doesn't make its money by selling memory so there is no reason for
"marketing disinformation".

Use of third party memory may result in intermittent parity errors.
Just how intermittent depends on a number of factors including but not
limited to the phase of the moon and sunspots.


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Dave Plummer, University College Hospital, London UK.

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