Friday, January 12, 2007

Memory errors at DDR2-960 MHz

I set the DRAM Frequency to DDR2-960 MHz in BIOS which equates to a 12:8 (DRAM:FSB) ratio with the CPU overclocked to 3.20 GHz (10x multiplier).

My Corsair XMS2 TWIN2X2048-8500C5 should be able to handle this easy. It is rated at PC2-8500 or DDR2-1066 MHz. According to its EPP (Enhanced Performance Profile) named "High Frequency" (Optimal Performance Profile), this memory can run at the memory speed of DDR2-1066 (memory clock speed of 533 MHz) at 2.2V with timings of 5-5-5-15 (CL-RCD-RP-RAS) with a Write Recovery Time (tWR) of 8T.

I ran Memtest86 v1.65 to test the new configuration and it failed with an error after 3 hours (or maybe sooner since I was not constantly monitoring the test.) I attempted to change the DRAM Write Recovery Time to 8 DRAM Clocks in BIOS.

Note that the EPP specified a Write Recovery Time (tWR) of 8T, but the ASUS 0804 BIOS allowed a maximum of 6T.

I had no other choice but to set the DRAM Write Recovery Time to 6 DRAM Clocks. I restarted Memtest86 v1.65 and it failed after 1 hour and 40 minutes with 2 errors.

I decided to loosen the memory timings to 5-5-5-18 (CL-RCD-RP-RAS) knowing that increasing the DRAM RAS# Activate to Precharge (RAS) setting to 18 DRAM Clocks would have very minimal impact on memory performance.

I ran Memtest86 v1.65 once more with the new memory timing and the test failed after 4 hours and 30 minutes with one error.

I believe that the only way I will be able to run this memory at DDR2-960 and up to DDR2-1066 is if the ASUS BIOS will allow DRAM Write Recovery Time (tWR) to be set to 8 DRAM Clocks as specified by the memory's Enhanced Performance Profile.

Given that the lastest version (0804) of the ASUS BIOS for the P5B Deluxe WiFi/AP motherboard does not allow this and maxes out at 6 DRAM clocks, I reset the DRAM Frequency to DDR2-800 MHz, memory timings to 5-5-5-15 (CL-RCD-RP-RAS), and DRAM Write Recovery Time (tWR) to 5 DRAM Clocks in BIOS. These were the last stable (error-free) settings for my memory.

I highly recommend that if you are running your memory at or close to its highest rated speed, check its stability by running Memtest86 overnight, specially if you have "Configure DRAM Timing by SPD" enabled to confirm that it is stable. If Memtest86 detects errors, disable SPD and set your memory timings manually according to your manufacturer's specifications.

I am perfectly content to run my Corsair memory at DDR2-800 MHz. This brings my attempt to optimize my memory settings to a close.

Next up will be overclocking my BFG 8800GTS video card.


tomhole said...

I am running COrsair XM2 DDR2 800 CL5 memory on my system. I can run it 1:1 (400FSB) at 4-4-4-12 and pass memtest overnight. If I up it to DDR950 and loosen the timings to 5-5-5-15, it will fail memtest after 3 hours. So, it is staying at DDR800.

As for overclocking, I went back to 3.2GHz (400 FSB x8 multiplier). 3.6GHz was not perfectly stable and still a little hot for my tastes. 3.2 GHz (400 FSB x8) is perfectly stable, idles at 33C, full Orthos load of 50C and full TAT load of 58C. That's good enough for me for 24/7 operation.

I wish I had your GPU. My 1650XT just doesn't have the horsepower to post anything over 4000 in 3Dmark06 and that's at 1024x768. Maybe in a few months when Vista comes out and the DX10 boards are out, then the 8800 series will come down to an affordable price.


Gerry said...

Respectable overclock!

ATI will have their DX10 graphics cards out soon. I am looking forward to this because I believe competition is good. This should bring prices down and drive performance even higher!