2 x TWIN2X40966400C5 does not run at spec

[MichaelD]

I have two kits of TWIN2X40966400C5 (4x2GB) in a brand new Asus PQ5 Pro Turbo running the latest BIOS. The two memory kits were bought at the same time and are rev1.3. Each 2-piece memory kit has sequential serial numbers. I.E. Stick 1 is xxx702, Stick 2 is xxx703. I have these "matched sticks" on the same memory channel. I.E. 702 in first yellow memory slot, 703in second yellow memory slot. Same with the second kit.

 

The memory should be running at 800MHz, but it's not. It runs at 816MHz and causes issues on warm reboots. I.E. the fans spin up but the board doesn't post. I have cleared the CMOS multiple times and have everything on Auto. Through trial and error I found that if I hard-set the FSB to 400MHz, then I get a solid 800MHz and no reboot issues.

 

I ran three passes of Memtest 4.10 and got no errors. Any ideas?

[Synthohol]

set it manually as you have done and dont give it another thought.

just to be clear, two memory kits are not "matched" unless all 4 sticks come in 1 package. then they would be factory tested as a 4 stick kit. mixing 2 kits is not recommended or suggested. see the link in my sig about 2 sets of ram.

[MichaelD]

OK, thanks very much Synthohol. I'll keep doing it this way then. Things have changed much over the years; you used to be able to throw any sticks in w/any sticks as long as the timings were the same.

[Yellowbeard]

I have two kits of TWIN2X40966400C5 (4x2GB) in a brand new Asus PQ5 Pro Turbo running the latest BIOS. The two memory kits were bought at the same time and are rev1.3. Each 2-piece memory kit has sequential serial numbers. I.E. Stick 1 is xxx702, Stick 2 is xxx703. I have these "matched sticks" on the same memory channel. I.E. 702 in first yellow memory slot, 703in second yellow memory slot. Same with the second kit.

 

The memory should be running at 800MHz, but it's not. It runs at 816MHz and causes issues on warm reboots. I.E. the fans spin up but the board doesn't post. I have cleared the CMOS multiple times and have everything on Auto. Through trial and error I found that if I hard-set the FSB to 400MHz, then I get a solid 800MHz and no reboot issues.

 

I ran three passes of Memtest 4.10 and got no errors. Any ideas?

 

If it was running 816 after a CMOS clear, then the ASUS BIOS was OCing the FSB slightly.