I have got a P5Q Pro Motherboard with a Core 2 Quad 9550 CPU. I got CORSAIR 4GB DIMM DDR2 800MHZ PC6400 CL5 (2X2GB) memory modules and the system worked fine (In QVL, 2GB CL5 Corsair modules are not mentioned). When I add another two modules (the same product) the system not boots(No output, system halt, the only thing which is alive is the fans which all work at the maximum speed ).
I re-checked the QVL list and found out that my options are very limited (with respect to both QVL and the currently available products in my reseller's stock). I want to focus on OCZ modules as it seems that it works better than the other modules. I want to have 4 X 2GB DDR 2 modules and it seems that I have two good choices:
a) 2X OCZ DDR2 REAPER HPC 4GB PC2-8500 (2X2GB) : I assume that those "N/A" fields in QVL (1066 MHZ) means that all models are compatible?? So, this one should be compatible in C mode (4X 2GB)
b) 1X OCZ DDR2 PLATINUM XTC 8GB PC2-6400 (4X2GB) : In QVL it is mentioned that 5-4-4-15 modules are compatible in A,B,C mode (However, this module comes in 5-4-4-18, will it make any problems?). Also it is mentioned that 5-4-4 2X2 GB modules will be compatible in A,B,C mode. Will this one also be compatible?
So, after all this, can you please confirm if a,b choices are compatible with my P5Q Pro motherboard and also which one do you suggest? (a costs around 20$ more)
Don't give up so fast on the Corsair, go to the Corsair configurator and see if your ram works with the P5Q, see link. Try this, make sure your 2x2 is in the A1 & B1 slot, boot up and set your values, voltage & timing, for now set your mem MHz to 667. It probably wouldn't hurt to bump your DRAM slightly higher to compensate for the extra dimms. Shut down and unplug the PSU. Discharge the motherboard by holding in the power button while touching the chassis for approx 30 sec. Add the 3rd stick to the A2 slot and see if it will post. If so, shut it down and discharge the board again then add the 4th stick and see if it will post. If you get this far you can start bumping up your mem MHz.
Thank you for your answer.
I checked out the website and it seems that my memory is compatible with P5Q pro (According to CPU-Z, it seems that my modules are TWIN2X4096-6400C5DHX )
I managed to get 3 modules to work using your approach, but as soon as I insert the 4th module, the system does not post!
Actually it posted one time but halted in a few seconds.
The 3 modules work also under 800 MHZ.
Isn't that a little strange? Should I expect this (supporting 3 modules but not the fourth)?
If i remember it right, by standard DDR2 should withstand up to 2.3v before permanent damage is caused, but for continous operation voltage below 2.1 is suggested. I ran my xms2 sticks at 2.1v for about 4 months, even though theyre rated at 1.9v, and they still work fine. And i believe your DHXs are nothing else but xms2 with DHX cooling
Anyway, what I questioned was not whether those 4 sticks can run at 1.8v but if theyre actually getting that 1.8v. Everyone will tell you that Auto settings are seldom accurate, so(if you have your ram on auto) try putting 1.8v manually first and if that doesnt help than try 1.85, 1.90, 1.95, you really dont risk anything here.