the new Athlon 64 architecture is unlike any other processor, and thus requires looking at things a little differently..
HTT (HyperTransport) is the new BUS architecture that AMD has been trying to work into it's systems for the past couple of years.. HTT is the bus on which ALL your components operate.. how the processor communicates with all the components on the motherboard. In the past, this bus was often the limiting factor in communications between the CPU, the Memory, the North / South bridges, and the graphics card.
A64 introduced more then one new way of thinking about CPU / Memory / and Motherboard architecture..
they also feature on core memory controllers..
the speed of communication between the CPU and the MEMORY is what was often referred to as FSB (200MHz / 266MHz / 333MHz / 400MHz), well that is no longer the case with the A64's, as the memory controller now opperates at core speed, just like the L2 cache.. the only difference is NO DDR memory exsists that can operate at core speed, so the memory must be run asynchonosly.. thus the lowest cpu:memory ratio possible with A64's is CPU:9 (ie 1800MHz core speed / 200MHz DDR Memory speed)
The HT 2x / 3x / 4x / 5x controls the speed at which the BUS operates, not at which the CPU/Memory operate.
I'm oversimplifying the whole affair, but someone may be able to post a link with a more through and detailed explaination.
5x HT = 1000MHz HyperTransport bus speed (ie 200MHz x HT setting)
HyperTransport offers such an increase in bus BANDWIDTH from previous BUS technology that there is no current performance benefit from running 3x HT (600MHz) vs 5x HT (1000Mhz)