HyperTransport
From Overclocking Wiki
AMD has a slightly different setup on their Athlon 64 and newer processors. They have eliminated the FSB altogether and switched to a hypertransport link. The design of the AMD processor includes a memory controller on board which dramatically changes the engineering of the board.
Although there is not a typical FSB in this case the overclock is handled in much the same way. Many users, in fact, still use the term FSB while talking about Athlon 64 based systems.
The Hypertransport (HT) clock is set by a multipier which is a ratio of the CPU's "FSB" clock. Its typical default mutliplier setting is 5x to the CPU's FSB setting of 200 MHz, which makes the HT clock = 1000 MHz. You do not want to push the Hypertransport bus over 1000 MHz typically as this can cause stability issues. So when you start overclocking the CPU by pushing the "FSB" clock over 200 MHz, you need to set the Hypertransport multiplier down so that it's resulting clock frequency is equal to or less than 1000 MHz. So you would want to follow this logic:
FSB between 201 and 250, then HT multi = 4x which makes HT clock 1000 MHz or less.
FSB between 251 and 333, then HT multi = 3x which makes HT clock 1000 MHz or less.
FSB between 334 and 499, then HT multi = 2x which makes HT clock 1000 MHz or less.
and so forth. Sometimes you can get away with a Hypertransport clock of over 1000mhz, but it does not yeild any performance gain over keeping it between 750 MHz and 1000 MHz, so all you're doing is adding risk of instability to your machine.
References to a HyperTransport speed of 1000MHz applies to all socket 939 and later applications. For socket 754 applications substitute the lower HT speed of 800MHz used in these CPUs and their supporting motherboards.
