XMS / Value Select Memory Compatibility

[Ohst]

Hi,

I currently have a 256MB XMS PC2700 memory module (Product code: cm64sd256 2700CX2h) in my system. I want to get more memory but can't find any of that specific memory available. I tried adding a 512 MB module of Corsair Value Select but only the memory in the first slot was recognized. Is there any way of using these two modules together? If not what memory would I have to get to still use the 256MB XMS module or would I be better of just getting all new memory? BTW I have a Asus A7V333 motherboard in case this makes any difference.

 

Thanks in advance,

Andy

[RAM GUY]

Please set the memory voltage to 2.7 Volts and then install the modules in slots 1-3 or 2-3 and set the timings manually to Cass 2.5-3-3-7 and test the system with http://www.memtest.org.

[Ohst]

Thanks Ram Guy!

My Cass was set to 2.5,3,3,6 and I didn't have the option of bumping it to 2.5,3,3,7 so I left it there. I couldn't find anywhere in the BIOS to set the mem voltage and after doing some research found I could only set the mem voltage by changing jumpers on the mobo itself (See below ). Of course this is all undocumented!!!

 

The default memory voltage of jthe A7V333 is out of spec which causes DDR DIMMs to run hot and eventually fail. The voltage can be adjusted by moving the undocumented jumpers JP1 and JP2 to close 1-2 or else remove both jumpers completely. We found the following voltages when measuring directly at the DIMM slots:

 

ii 2.59 - 2.63V (same with one or both jumpers removed completely)

i! 2.78 - 2.83V (default setting, out of spec according to JEDEC guidelines

!i 2.88 - 2.94V

!! 2.95 - 3.06V

 

The latter two settings are almost guaranteed to destroy the memory modules. We found that by reducing the voltage from default to the lowest setting, we were able to achieve approximately 3% system performance increase (not in SiSoft Memory benchmark, though but in real applications)

 

We found that running the memory bus asynchronous at 166 MHz with the FSB does not overall increase system performance because of the higher latencies and the buffers required for synchronization of memory and FSB.

 

I went ahead and set the mem voltage to the first configuration (ii) like it suggested. Finally I moved the modules to the 2nd and 3rd slots and WA-LA I now have 768MB of memory.

 

Thanks again for puting me on the right track!