I have a Dell OptiPlex 755, 4 slots on Mobo. Two slots are each filled with 1GB DDR2-6400 non-ECC, and the timings are 6-6-6-15 according to memtest86+.
Today I tried to put two OCZ 512mb's in slots 3 & 4, and the Dell freaked out. The timings are 4-5-4-15. I assume that mixing the two different timings cause the Freak. By "Freak", I mean that the Mobo did an alarm sound and wouldn't even attempt to load to the BIOS.
BTW, I did run the Dell with the OCZ only and it was fine and passed MemTest, so the ram is OK.
So I'm on the hunt for ram for slots 3 & 4. The QUESTION: do I have to find ram with identical timings? Would 6-6-6-12 work along side of 6-6-6-15 ram? I see the 6-6-6-12 a lot on Fleabay.
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More abouthelp mismatch question
Try with the OCZ RAM and set it in BIOS to 6-6-6-15, save the new configuration and then put the other RAM in.
The Dell BIOS offers ZERO memory manipulation (this is a business PC used for software development). I did download the latest BIOS hoping they added it, but no go.
BTW, I was wrong, the existing Dell (Hynix) ram is 6-6-6-18. SO, to add more ram, does it have to be exactly 6-6-6-18?