I have tried just moderately OC to ~2.6GHZ, by setting the FSB to 240 from default 200 and then changing the System Memory Multiplier to 3.33 to give the 800 for the DDR2 800 RAM.
CPU clock ratio is kept at default 11x (the highest)
However, after saving and exiting bios, the computer reboots and goes back to the stock settings.
Am I not doing something that I should be doing?
More about :gigabyte g33m s2l reverting stock settings
The good news is that Gigabyte Core2 motherboards will try to reset themselves into a bootable configuration automatically. The bad news is that your motherboard really did not like your OC settings.
Here's what happened:
Lets assume that you left your memory settings on Auto. At an FSB freq of 240 MHz, your memory will be running at (240/200*800 MHz) or DDR2-1000 speeds.
Now, the 3.33 mem multiplier should work. The memory should be operating very closely to 800 MHz. But you are mixing memory.
My suggestion. Set the RAM voltage to 2.2 volts or "nominal +0.4 volts". Set your System Memory Multiplier to 2.0. Your memory will be running slower than its rated speed, but the 1:1 FSB:RAM ratio will give you increased stability without costing much performance.
I tried your suggestion with system memory multiplier to 2.0, and so it came out to (240MHz x 2) = 480, at both 2.1V and 2.2V and it still did the same reboot.
I have also tried tinkering with different settings. I can change the voltage all the way up to 1.4V (default 1.325V) and it's fine. I can also change the system memory multiplier, and it works. Right now the RAM is at 5-5-5-15 and 1.9V stable.
It's just if I change the FSB, even by a tiny bit, like up to 210MHz from 200, after F10 save/exit, it restarts with default settings, and I can't figure out why. It feels like there's some setting that I'm missing
I have tried booting with just one set of RAM as well (at various settings), and had the same exact problem.
I switched in this set
Corsair XMS2 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel Kit