RAM Compatibility issue

[sglanton]

A few months ago, I bought CORSAIR XMS2 2GB (2 x 1GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) - TWIN2X2048-6400C4 from Newegg.com.

Since then, it has been performing perfectly.

A couple days ago, I bought 2GB more, to install 4GB total into my computer.

Since then, I have had nothing but problems. It consistently locks or crashes.

Occasionally I get the blue screen of death. However one time, I noticed the blue screen stated something about compatibility with my RAM.

Since its the same RAM, how could there be an issue?

I am currently running Windows Vista Ultimate, and the motherboard is ASUS M2N32-SLI Deluxe Wireless Edition AM2 NVIDIA nForce 590 SLI MCP ATX.

 

Please advise.

Thank you.

[DerekT]

The on CPU memory controller can not keep up with the extra DRAM at the rated 6400 speed. You will need to drop the speed of the DRAM from 800Mhz to 667Mhz. If you had purchased 4 X 1024MB of PC8500 (1066Mhz) DRAM, then you would have had to drop to PC6400 (800MHz) DRAM, etc. 2 X 2048 will not issue this problem. This is a problem of all 4 banks being populated and is related to the chipsets inability to access the now doubled banks.

 

Think of it this way. If you have a small phone book, then when you go into the index to find the page where you will find the phone number you are doing so at a certain speed due to the pages of the Index. Then you have to drive through the pages to get to the number. Now if your index is twice as large and the pages twice as many, then it takes longer to access the data. Now DRAM has a Strobe and the length of the strobe is how long the rows and columns can be left open before they must be refreshed. There is not enough time for the dram to be refreshed and then accessed with 4GB at the full access speed of the DRAM. The chipsets are optimized for 2GB, not 4GB and for 2 DRAM slots, not 4 DRAM slots populated.

 

You can overclock the FSB (and hence the on chip Memory Controller) to gain some extra bandwidth, and thus access the capabilities of the DRAM since the chipset is now clocked up. Usually when you clock up the FSB and concurrently the on CPU Memory Controller you need to raise the voltages of the CPU a bit as well.

[sglanton]

The fix seems easy enough, however your deeper explanation makes it seem to me that maybe it wouldnt help the computer to have 4gb vice 2gb. Is this correct? Or just that all 4 banks are filled instead of just 2? Meaning that 2 x 2046 is better than 4 x 1024??

 

Thanks tons for your assistance!

[DerekT]

The fix seems easy enough, however your deeper explanation makes it seem to me that maybe it wouldnt help the computer to have 4gb vice 2gb. Is this correct? Or just that all 4 banks are filled instead of just 2? Meaning that 2 x 2046 is better than 4 x 1024??

 

Thanks tons for your assistance!

 

You have a good understanding of the issue. The problem is one of DRAM access time due to the doubled banks of DRAM. The problem is not DRAM module density so yes, 2 X 2048 is better than 4 X 1024. I also believe that 2 X 1024 is usually better in a 32 bit system than 4 X 1024.