quick question about a64/opteron's FSB

[jjyiz28]

i know the memory controller is on-die the cpu chip. and the bus is the same as the cpu speed.
so since the a64 is 2ghz, its fsb is 2ghz?? and theoretically if the speed of ddr is at 2ghz, then it would be the same as L1,L2 cache speeds?? so there would be benefits the higher ram is used, ie going from ddr400, to ddr500, etcc..untill ddr2000(hypotetic)

 

[Jeff7181]

No... there is no FSB... the internal clock speed is derived from the HyperTransport Link which operates at multiples of 200 Mhz ranging up to 800 Mhz, and it's double data rate... that's where the "1600 Mhz bus" comes from. And since the memory controller is onboard, you can't increase the speed of the ram, at least not to my knowledge, and the Athlon-64 only supports up to PC3200 memory right now. It will take future core revisions to allow the use of faster memory... or... possibly they can find a way to do it through a BIOS update, but that's unlikely since like I said, the memory controller is on die.

 

[Soulkeeper]

the fact that the memory controller is integrated just means lower latencies for the lucky ones that have such a system

 

[jjyiz28]

clock speed derived from HT link... since it operates at 800mhz, its means for A64 2.0ghz, its 800*2.5 = 2000mhz?

 

[rgreen83]

The fsb bus is now just known as the memory bus on athlon 64s. The memory controller is located on die so its speed is determined by the cpu speed, but the actual bus from mem controller to memory is still the same speeds like 166 or 200mhz ddr, the bus speed is configuable in the bios.

The hyper transport is what many website are referring to when they say fsb speeds on the athlon 64. This is actually determined by the bus width on the motherboard. The NF3-150 boards use a 600 mhz hyper transport link (which is bi-directional since it is a serial-not parallel-link). The VIA kt800 chipset however uses the 800mhz hyper transport link, with it being bi-directional (800 up, 800 down) this is why you will read many places calling the fsb on the A64 1600 mhz since every discreet aspect of the motherboard other than the memory is interfaced over that hypertransport link.