FSB Hole and FSB Strap

I would like to say a few words about FSB Hole right away: we found no frequency intervals where ZOTAC nForce 790i-Supreme mainboard would be non-operational. However, they do exist or at least existed. Here is what they say about the BIOS P05: "Fix isolated corruption issues around certain non-stock FSB/DDR3 configurations near 1600 MHz". So, there were some problems around 400 (1600) MHz but they were eliminated.

As for FSB Strap, when at some point during overclocking performance drops, we checked it out by testing the read speed from the memory subsystem in Everest program. The memory divider and timings were locked, the processor clock frequency multiplier was reduced to x6. We used a dual-core Intel Core 2 Duo E8400 processor, which ZOTAC nForce 790i-Supreme mainboard can overclock to 510MHz FSB. So, we started testing at this frequency and then got 10MHz lower with every step. The memory frequency reduced accordingly, and so did the read speed. Everything went on nice and easy until we hit 450MHz FSB, where performance suddenly jumped up.

We took a closer look at this problem and found out that the performance drops when we move from 450MHz to 451MHz FSB. AT 450MHz FSB the read speed is 8295MBps, and at 451MHz it drops to 7054MBps. This notorious threshold didn’t go away, no matter what memory timings or dividers we set. Only the absolute read speed value changed, however, it still dropped down dramatically when moving from 450MHz to 451MHz FSB.

The saddest thing is clearly seen from the graph above: overclocking doesn’t make up for the performance drop. Even when we are at maximum 510MHz, FSB the read speed is lower than it used to be at 450MHz. So, it doesn’t make sense to overclock past 450MHz on ZOTAC nForce 790i-Supreme mainboard. So, looks like we won’t be able to really enjoy its good dual-core and excellent quad-core processor overclocking potential.