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Need help w/ HyperTransport understanding

Last response: in CPUs
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November 20, 2004 1:03:12 AM

I am just starting to do research for a new computer build and I am leaning towards an AMD64 computer. However, I am somewhat confused with the HyperTransport bus. What is it? I know it isn't the FSB. Do AMD boards have an FSB? Is it related to the HyperTransport bus? Would I want my memory to be synchronous with the HyperTransport bus?

Any info would be appreciated. Feel free to be as technical as necessary.
November 20, 2004 1:26:23 AM

The HTT bus is amd's new and improved fsb. Memory access has been changed to it's own bus, while the HTT is faster, and is more bi-directional.
The memory speed will not likely ever catch up to the HTT bus, but having memory that is slower than the memory bus, does take a hit. The latest HTT bus is 1ghz each way, while the memory bus is still running at 200mhz, with DDR, for an effective rate of 400mhz. There is also dual channel, on s939, which doubles the potential memory bandwith.
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November 20, 2004 11:14:31 AM

I know its different for the XP chips (staggers latencies) but for the Athlon64/FX chips it might be the same as the P4 chips. Ask crash.

On the topic of the FSB, FSB is generally used to tell us the speed that the CPU connects with the northbridge.
Since the Athlon64 range of CPU's doesnt have a northbridge (its memory controller is on the CPU instead) then technically it doesnt have a northbridge. Instead it has a southbridge where all the peripherals are connected (PCI slots, USB, AGP etc) This southbridge is connected to the CPU Hypertransport link. The memory is connected to the CPU on a different bus.

You will ofter hear that the hypertransport link runs at 1.6Ghz-2Ghz. This is a marketing slogan, it if fact runs at 800Mhz-1Ghz but it is FULL DUPLEX. This means it can send data in both directions at the same time. The intel pentium4 bus is only half duplex.
November 20, 2004 4:30:56 PM

Ok. HTT (HyperTransport bus) is the connection speed to the southbridge, which connects to the PCI bus, AGP, etc, right? And the memory, controlled by the AMD chip, is connected to the chip via a different bus, which does not run at the same speed as the HTT. So, if I have a 1 GHz HTT, I do not need to have DDR 500 memory or anything like that, right? A stock speed AMD64 chip will use DDR400 and no more.

Please correct any of the incorrect statements above. Thanks again.
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