Someone explain HT please

[mobbo]

I just got my first AMD Athlon 64 processor (3000+) Socket 939 in the 90nm core. The motherboard I have (GigaByte K8NS-939) has an nForce 3 Ultra chipset. Now, my understanding is that the HT can run at up to 2000MHz with my processor and the chipset on my MB. The RAM I have is 2x512MB PC3200 Kinsington HyperX running dual channel. I have nothing overclocked, so the RAM is running at 200MHz.

Now, my true question is: what is my HT running at? Again, the RAM is running @ 200MHz dual channel and the HT multiplier is 5x. My understanding is it is running at 2000MHz (200MHz RAM freq x 5 HT multiplier = 1000Mhz x 2 RAM clock cycles (DDR RAM) = 2000MHz). But I have read so many contradicting things I cannot be 100% sure! Thanks in advance for clearing things up.

 

[stevty2889]

Your calculation is almost right, except for the part where you are adding in the ram to your HTT. HTT is like the FSB with P4 systems..the speed of your ram has nothing to do with the speed the HTT is running at. It is running at 1000mhz (200mhz x 5).

 

[gobucks]

the 2000MHz figure comes from the fact that the HT link is 16 bits upstream and 16 bits downstream, so the theoretical bidirectional bandwidth is 2000MHz. I personally think that's misleading, and usually refer to it as 1GHz. As for safe HTT speeds, you should be fine up to about 1100-1200MHz, at which point things start to get hairy. So if you're overclocking, you should probably take your HTT link down to 4x, maybe even 3x if you OC high enough. I currently have mine at 4x with a core speed of 283MHz, so my HTT link is funtioning at 1133MHz without problems, although your actual mileage may vary.

Also, when thinking of HTT, don't think of it as a traditional FSB. Unlike the P4 and AXP, the memory controller is located on the CPU itself, funtioning at full CPU speed, and has an independent link to the memory banks. It does not go through the FSB at all. This proves to be very efficient, as you can see in any memory bandwidth benchmark of a socket 939 CPU. Anyways, since the CPU takes care of memory accessing, which makes up the majority of FSB work, the HTT link only has to take care of the remainder of bussing duties. In the Opteron 2xx and 8xx chips, the HTT link is quite important - it provides an independent link to the other CPUs. In fact, the 2xx has 2 HTT links, and the 8xx has 3, so that 1 can be used traditionally, with the rest linking to CPUs. This is why opteron competes so well with Xeon - opteron is virtually swimming in bandwidth, while Xeon has to share all memory access AND inter-CPU communication via its single 533MHz or 800MHz bus. Anyways, moving right along, on the desktop, the HTT link handles more menial tasks. Shuttling data from things like SATA/PATA HDD controllers, PCI/PCIe/AGP busses, LAN connections, etc. are the majority of these duties. None of these are particularly intensive, since the only high-bandwidth thing on the bus is a PCIe x16 link (4.0GB/s) or AGP8X (2.1GB/s), and the HTT link has 8.0GB/s to work with. On top of that, even a 6800 Ultra or 5850XTPE will have trouble saturating even 1.0GB/s. So that means the HTT is WAY faster than it needs to be. Overclocking it is pointless for its own sake, and underclocking it won't change anything until you start to hit speeds like 600MHz or below, where performance might drop slightly (see nforce 3 150 reviews).