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HyperTransport Question...

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June 10, 2006 12:08:01 AM

When it says HyperTransport technology allows up to 2000MHz system bus, I assume that doesn't mean the processor will run at that frequency. What does the Venice core 3800+ run at? Is it 200MHz x 4 = 800MHz or 200MHz x 5 = 1000MHz effective? I'm confused about these numbers...sometimes I'll see 2000MHz, sometimes 1GHz, and I've seen the 800MHz figure too (I am wondering if the 800 figure is wrong)...
June 10, 2006 12:12:38 AM

Quote:
When it says HyperTransport technology allows up to 2000MHz system bus, I assume that doesn't mean the processor will run at that frequency. What does the Venice core 3800+ run at? Is it 200MHz x 4 = 800MHz or 200MHz x 5 = 1000MHz effective? I'm confused about these numbers...sometimes I'll see 2000MHz, sometimes 1GHz, and I've seen the 800MHz figure too (I am wondering if the 800 figure is wrong)...


It runs at 2000MHz just as its listed. AMD does things differently than Intel. There is no front side bus, as the memory controller is intregrated on the CPU. So the CPU takes directly to the memory, not to the northbridge which then talks to the RAM on Intel systems.
June 10, 2006 12:21:35 AM

Ok. How does this work if your motherboard says it supports HyperTransport and 1000MHz Front Side Bus. Is it 2000MHz effective?
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June 10, 2006 12:35:52 AM

Yes it is 2000MHz effective.
June 10, 2006 12:44:13 AM

Thanks guys. Do pretty much all Sckt 939 Athlon 64 mobos say 1000MHz FSB?
June 10, 2006 12:46:27 AM

Quote:
Thanks guys. Do pretty much all Sckt 939 Athlon 64 mobos say 1000MHz FSB?


No, some older ones only support 800/1600.
June 10, 2006 12:59:31 AM

I see.

How come sometimes when I google Athlon 64 3800+ Venice I will see 800MHz FSB by the name?
June 10, 2006 5:00:11 AM

Also, with the 3800+ and a 1000MHz mobo and 400MHz DDR memory, will the timings be 1:1?
June 10, 2006 7:33:12 AM

Yeaaaargh, need a full explaination me thinks.

Ok, first off is your base clock, we'll call this your HTT. This is the clock that everything else is derived. For most if not all motherboards this is at 200MHz. When overclocking you raise this value.

Next off is your hyper transport and by default it is 5x your HTT but you can lower the multiplier when you raise your HTT because you generally don't want to overclock the hypertransport. Most vendors give the 2000MHz value because your hyper transport is double pumped (2x 1000MHz)

Your CPU speed is derived from the HTT and is the product of the multiplier and the HTT speed. Say for a HTT of 200MHz and CPU multiplier of 10 you get a processor speed of 2000MHz.

Your RAM is also derived from your HTT. By default when you buy RAM it runs 1:1 of your HTT. It doesn't matter what RAM you buy it runs 1:1. However, DDR333 RAM won't work at this speed (as it can only run at 166.5MHz). So you have to use a 1:5/6 divider. Thus your RAM runs at 200MHz * (5/6) = 166.5MHz.

The reason why sometimes we have to use dividers for our RAM is because we are overclocking. If we decide to increase our processor to 2400MHz then we have to put our HTT to 240MHz. This, however, means we are running our RAM 40MHz (If we are using DDR400 RAM) out of normal speeds and we may well need to use a 1:5/6 divider (240MHz * 5/6 = 200MHz).
June 10, 2006 6:46:40 PM

Thanks, Kholonar. Very helpful.
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