Step One: Maximum Stable CPU Speed
One of the problems we encountered in previous motherboard overclock testing was an early BIOS revision that had not yet been fully optimized for FSB stability. Updating it to version F9 was easily accomplished using a USB thumb drive, made bootable via Hewlett Packard's USB Format Utility and set as first hard drive in BIOS.
We disabled unused CPU features and those that would otherwise contradict our manual frequency and voltage selections.
The first step in finding the highest CPU speed is to make sure RAM remains stable. We used lazy 5-5-5-15 timings with the chipset's lowest "2.00 memory multiplier", a setting which is actually 1.0 times the CPU FSB, and misnamed as a ratio of memory data rate (DDR) to FSB clock rate.
Next, we increased CPU core voltage to 1.45V, DIMM voltage to +0.4V (2.20V), and Northbridge voltage to +0.3V (1.55V).
Knowing the relatively high limits of our CPU, we jumped directly to 366 MHz before following our recommended 8 MHz steps between stability tests. This was where our first test deviation occurred: some speeds between 380 MHz and 400 MHz were unstable, while other higher speeds were perfectly fine. Increasing FSB voltage by 0.20 V got us past 420 MHz, but again, with some settings in the middle not working correctly. Choosing the +0.30 V setting eliminated all FSB stability issues and allowed us to shoot for the moon!
Notice that we have not yet increased the PCI Express voltage. We tested the setting to see if it would improve Southbridge stability, but the CPU still reached the same limit.
You'd like to see that limit, right?
We're seeing a lot of 2 MB cache Core 2 Duo chips reaching similar speeds at voltages similar to our 1.45 V setting; your later-revision core may do even better than this early B1 S5 stepping. Congratulations to Gigabyte's BIOS team for turning this into a serious overclocking board.
