Disparity in reported FSB on A64 Chipsets

[SBGTF]

I was comparing some motherboards over at Gigabyte and I found the following listed FSB speeds.

nForce3-250 = 1600MHz FSB
nForce3-150 = 1200MHz FSB
VIA K8T800 = 800MHz FSB

Everything I've seen seems to indicate these three chips perform about the same, so I can't understand the disparity in FSB speeds.

The Hypertransport of the A64 is 800MHz as far as I know. All of these were reported for Socket 754 boards (single channel, as far as I know).

 

[DAPUNISHER]

It's not really an fsb but the HTT speed and the rating is based on being double pumped. The K8T800 does the full 800mhzx2=1600HT the nF3 150 is 600mhzx2=1200HT and only 8bits upstream instead of the full duplex 16bit up&down the Via, SiS, and AMD8151 can. The nF3 250GB supports 1000HTx2=2000HT and K8T800 pro can as well. As you mentioned, there hasn't been a clear performance advantage in benchmarking between the 150 and K8T800, but I've read that if you start loading the bus up the Via's superior throughput capabilities would give it an advantage.

I've been using a nF3 150 board, and had a AMD8151 full duplex chipset before that, I've experienced no noticeable performance degradation and I reduced the HTT speed to 2.5x200=500HTT then pumped it up to 240HTT which is calledLTD speed= Lightning Data Transport on the nF3 150 for the stock 600HTT and the added CPU speed has made for a nice boost. My board even has the 4x multiplier for the HyperTransport but I can't say if it can do 1600mhz since I didn't really play with it.

 

[Peter]

It's not a front side bus, it's just an I/O link. The actual clock rate should be 200 MHz, soon to be raised to 250. NVidia's original offering had that at 150 (hence the names!), and also had just an 8-bit link in one direction. Everyone else has 200 MHz 16-bit links either way.

Why the inflated numbers then? Well, it's 200 MHz, DDR, bi-directional, 2 bytes wide. Them marketing folks think that entitles them to call it 1600 MHz.

Performance degradation from slow HT links is not visible unless you're going for some serious 3D work with lots of AGP traffic, or server jobbies with a lot of I/O traffic. But for the latter you don't want to use anything but AMD's chipset for its twin PCI-X busses anyhow.