I have been trying to overclock my i7-870 system for several weeks. I can't seem to get anything stable over 3.6Ghz. Here is my system configuration.
4x2G Mushkin PC3-12800 (running at 2196Mhz 7-10-8-24
HIS 5770 1GB Video Card
Linksys Wireless NIC
CPUx = 20
CPU @ 3.651 Ghz
MEMx = 12
MEM @ 2191Mhz 7-10-8-24
Vcore = 1.275V
Vvtt = 1.176V
Vdram = 1.65V
Vpch (1.8) = Auto
Vpch (1.05) = Auto
My testing process is to use Prime95, IntelBurnTest & memtest. I have found that Prime95 and IntelBurnTest identify stability issues. I used memtest to make sure I could operate my memory at the overclock speed of 2191.
The above settings have tested overnight with Prime95 without errors.
I have discovered that sometimes I need to decrease Vtt to gain stability when increasing CPU speeds. For example I used Miahallen's 3 Step Overclocking Guide as a starter. I found that for a stable 180 BCLK in step 1 required Vtt=1.197, I ran the test up to BCLK=210 and that required Vtt = 1.298.
I used that Vtt for step 2 and found my stable memory frequency at 2:12 with 2166 @ Vtt=1.309.
What is strange is that I could not get this configuration of Vtt=1.309, 2:12 Memory stable when I was trying to increase the CPU speed above 3.4Ghz. I ran Vcore up as well as increasing Vtt. However I did find that by reducing Vtt and Vcore I could get a stable 3.6Ghz configuration.
Now I am trying to get the CPU even higher to 4.0Ghz (22x) but am unable to get the system stable.
I have tried to play with Vpch (1.8) and Vpch (1.05) and slightly increased them to make the system run longer at 3.8Ghz however the system still fails after about 1 hour.
I have done a lot of searching but have not discovered any guidance on the two last voltages and how they affect stability. Vpch (1.8) and Vpch (1.05).
All I know is that they seem to increase it, if I push them up too high they reduce stability. Also I find it strange that reducing voltages increase stability with higher clock speeds.
More about :msi p55 gd85 overclocking pll voltages
1.443V Vcore (BIOS setting, actual voltage at chip = 1.4v idle, 1..33v 100% load)
1.25V Vvtt (BIOS setting, actual voltage at chip = 1.277v Idle)
1.9V Vpll (BIOS setting, actual voltage same)
1.05V Vpch (BIOS setting, actual voltage same)