I'm fairly new to this but I'm having an intermittent problem with prime95 and memtest.
I have an unlocked AMD Phenom II X2 550 which is now an X4 B50 and has been running fine on a desktop PC with Windows 7 Home Premium without any problems. I decided to have a go at overclocking it and decided to run prime95 blend test before I started just to make sure everything was OK. It failed after about 15 minutes with a rounding error on one of the 4 cores. Initially I thought this was a possible CPU problem and one of the unlocked cores was faulty. Having run the test a few times it seems to fail on a different core each time taking anywhere between 15 minutes and 3 hours.
I then decided to check the memory. I have 4 x Corsair VS2GB1333D3 2GB and while all 4 sticks have the VS2GB1333D3 designation on the sticker two are reading on my system as VS2GB1333D4. I ran memtest and it didn't find any errors with the memory so I tried upping the processor Vcore voltage slightly to see if that would stabilize the processor. Prime95 blend test failed again so I ran the small FTT test and it ran without a problem.
I tried re-arranging the memory on the board to group the D3 and D4 sticks together and ran memtest again. This time I got an unexpected interrupt error. Ran it a second time and there were no errors.
I'm not sure where to go from here. Is this definitely a problem with my memory or could it be the motherboard (M4A785TD-M Evo)?
You can first try adding +0.05v to the DRAM Voltage, or in other words set the DRAM Voltage -> 1.55v and maybe 1.58v.
Failure, then boot (1) stick at a time to find the 'bad' stick.
VS2GB1333D3 - is NOT a matched kit and they're individual sticks. I only recommend fully matched kits that come as 4x2GB*.
VS2GB1333D4 - different 'internal' version I assume; mixing different IC's can cause problems.
CPU | D4 | D4 | D3 | D3| ; D4 = black and D3 = Blue or visa versa.