Hello, strange problem I have here, or maybe I don't understand what I'm doing exactly.
I have an EVGA SLI Motherboard (758) running a i7 920, using Corsair PC12800 RAM. I bought 12 GB (yes I know, overkill for most purposes) and installed it, ran just fine. Overclocked the i7 to 3.6 ghz, rock solid. My problem is the memory and what happens when I try to run it at anything over 1067 mhz. If the timings are set at 2:10, giving an effective 1833 or so Mhz to my memory with that overclock, my computer posts but doesn't leave the initial post black screen, total freeze. So I figured I should raise memory voltage, went from 1.49 in .1 increases up to 1.65, still no go, no matter what. So I lowered the timing to 2:8, giving an effective 1447 MHZ to the memory, below what it's rated at, and this is where it gets really weird : My computer posts and boots to Windows (7 64 bit btw), but in msinfo the computer recognizes that 12 GB are installed, but only says 8 GB are available.
So, I increased voltage at 2:8 slowly up to 1.65, same issue, system won't use 33% of the available memory. Then, figuring 12 GB was just too much for my system to handle (wouldn't see why that'd be the case, though) I pulled 3 sticks. When I was down to 6 GB if I set timings at 2:10, no go at all, and at 2:8 still lost 33% of available memory (msinfo cites 6 GB installed, 4 GB "available").
Only when I lower timings to 2:6, giving an effective 1067 MHZ to memory all the memory is there and available, whether I install all 12 GB or only 6. Not only that, but I don't have to touch voltage at all, the auto defaults to 1.49 and everything is rock solid. I ran memtest, memory seems good, and considering the steps I've taken I don't think this is a voltage issue with VDIMM itself.
Is there some other voltage I need to be increasing when I try to increase the timings on the memory? Has anyone ever had this issue where at certain timings the computer "sees" the installed memory but won't use it all? Thanks for any advice that anyone can give me!