SiS 756: PCI Express for AMD Socket 939

Overclocking: SiS 756 Reference Board

SiS 756 Reference Board
Overclocking Testbed
Processor:	Athlon 64 4000+ (2.4GHz, 1MB Cache)
CPU Voltage:	1.55V (default 1.50V)
Cooling:	Thermaltake Silent Boost K8 Heat sink/Fan
Power Supply:	OCZ Power Stream 520W
Memory:	OCZ PC3200 Platinum Rev. 2 (Samsung TCCD Memory Chips)
Hard Drive:	Seagate 120GB 7200RPM SATA 8MB Cache
Maximum OC: (Standard Ratio)	220*x12 (4x HT, 2.5-3-3-8) 2640MHz (+10%)
Maximum FSB: (Lower Ratio)	220* x 9 (4x HT, 1T) (2640MHz, 2 DIMMs in DC mode) (+10% Bus Overclock)

*The SiS 756 Reference Board artificially resets the clock to 220 with any setting above 221. This happened with both the stock multiplier (12X) and lower multipliers down to the lowest board multiplier of 8x.

It wasn't enough that the settings for testing overclocking were very limited on the SiS 756. The board artificially set higher clock settings back to 220. We thought that we were testing at 233 CPU clock until we ran CPU-Z, which told us that the board was running at 12 times a clock frequency between 219.5 and 220.3. SiS would have been better to let the board fail overclocking naturally instead of manipulating clock frequencies.

This same phenomenon was seen when we tried to lower multipliers and crank up to the board max frequency of 255. The SiS 756 Reference either dropped to 220 or lowered the multiplier to 133 or both. As a result, we could find no way to clock higher than 220 (+1-%) at any ratio. All-in-all, this was one of the most disappointing performances that we have seen in overclocking a Socket 939 board. Perhaps SiS is actually shipping 756 chipsets with better OC potential. We certainly hope that they are.