Mixing Memory speeds?

[Jude]

I recently upgraded a two+ year old MSI KM2M Combo/Athlon XP 2400+ system, and one of the new parts added was a Corsair VS512MB266 memory. The upgraded system ran fine for about 5 weeks, then started having flakey problems at an increasing rate. It got so bad that I couldn't gather 700 megs of files for a CD burn without getting errors in two or three files. The errors were always single-bit errors, and were always a zero bit instead of a one in the lowest bit of a byte.

 

After much hair-pulling, I believe the problem is the new memory: 2 hours of Memtest-86 v3.2 turned up over 1600 errors, which occurred slowly at first (half hour before first error), and then more rapidly as time passed. Most of the errors were the same syndrome (zero instead of one in lowest bit of byte) that I had observed when manipulating files. Testing was done with only the new memory installed.

 

With only the original 256Mb memory installed, the system runs fine (no weird errors) and it also passes 2+ hours of Memtest-86 with no errors.

 

The reason I posted this in "compatibiity" is that I noticed that the original memory is labelled as PC-3200, but I believe the new VS512MB266 is only PC-2100. I thought the new memory would be appropriate for my mobo, but finding that the older memory was PC-3200 has made me wonder. FWIW, the system is not overclocked, and the BIOS settings are all defaulted.

 

I'm also wondering if installing two different speeds of memory in one system is such a hot idea, and what I should do with my apparently-bad new memory. If I get the bad memory replaced by good, it will still be PC-2100 and I'm not sure if I should put that in a system that has run very well with PC-3200. I'm particulary uncomfortable with the idea of installing both PC-3200 and PC-2100 at the same time.

 

I'm just looking for advice about what I should do at this juncture.

[RJLeong65]

It is a bad idea running memory at a faster clockspeed than your processor's FSB clockspeed on any Socket A system. Your system will likely run unstably under such circumstances.

 

Your Athlon XP 2400+ uses a 133MHz FSB clockspeed (equivalent to a "266MHz" FSB). Therefore, your memory must also run at 133MHz for optimal stability and performance. As a result, you must go with PC2100 DDR memory for your system (or manually set your PC3200 memory to run at only 133MHz/DDR266). PC3200 memory has an actual clockspeed of 200MHz - 67MHz faster than your processor's FSB clockspeed. And the farther away from synchronous, the greater the risk for instability and performnce degradation.

[RAM GUY]

To add on to RJ's comment:

 

You may not need to set the PC-3200 RAM to PC-2100 manually as it will cycle itself down to this speed if the CPU FSB is already set to 133. However, if you have your RAM manually set to 200Mhz FSB then you will run into problems.

[RJLeong65]

To add on to RJ's comment:

 

You may not need to set the PC-3200 RAM to PC-2100 manually as it will cycle itself down to this speed if the CPU FSB is already set to 133. However, if you have your RAM manually set to 200Mhz FSB then you will run into problems.

 

It depends on the motherboard's BIOS. Some BIOSes will try to set a 200MHz memory speed even with a CPU FSB of 100MHz unless you manually override the autodetected setting.

[RAM GUY]

It depends on the motherboard's BIOS. Some BIOSes will try to set a 200MHz memory speed even with a CPU FSB of 100MHz unless you manually override the autodetected setting.

Agreed RJ, but with his board this will not be the case.