Been a while.....

altec · May 27, 2005

Been a while....

Ok, I have read through Gautam and hitechjb's stickies, and I am still not really understanding how the A64's derive their clock speeds with the HTT, multipliers and all of that. I am very fluent with the XP systems, but I have been out of the loop since the 1700+ reigned king of overclockers.

Any help with working through the A64 architecture and overclocking techniques would be greatly appreciated....

Glad to be back...... :eh?:

Gautam · May 27, 2005

Hey welcome back bro!

If we're strictly talking speeds, you could look at the HTT as if it were the FSB..

HTT x CPU multiplier = CPU speed, i.e. 9x200=1800, 200 is the HTT speed.

The main difference between the FSB and the HTT is that the HTT doesn't actually carry any data; its just a number.

The memory speed is then derived off the CPU speed, at 1800MHz you could have 180MHz with a CPU/10 divider, 200 with a CPU/9 divider, 164MHz with a CPU/11 or 225MHz with CPU/12 for instance.

That's whats really important. The HyperTransport bus is analogous to the FSB, sort of, but you don't usually have to worry much about it.

zer0nix · May 28, 2005

Gautam said:
The HyperTransport bus is analogous to the FSB, sort of, but you don't usually have to worry much about it.

<butts in> if you don't mind, could you please explain it to me? i'd first heard about it a few days ago when someone stated that to stabilize certain clocks one should lower their 'ht'/hypertransport multiplier from 4 to 3 and i'm still not too sure what they were talking about...

LoneWolf121188 · May 28, 2005

HT bus can't be over 1000 (800 on older A64 mobos). It's derived from the HTT bus. HTTxHT Multi=HT speed. If you raise your HTT from 200 (stock), to say, 220, but don't change the HT Multi (aka the LDT), your HT bus will then be 1100, which is way out of spec and can be problematic.

The thing about the HT bus is that its not really that important to have high speeds on it. 820MHz (205x4) is actually better than 1025MHz (205x5) becuase its more stable. The HT bus is so HUGE that it will NEVER become saturated (a bottleneck), unless of course you run it at like 300MHz.

A64 OCing in a nutshell:
HTTxCPU multi=CPU speed
HTTxLDT=HT bus speed
CPU speed/RAM divider=RAM speed
And thats about it!

Moto7451 · May 28, 2005

I saw some benchmarks that showed that there is less than 1/10th of a percent difference between an Hypertransport Bus speed of 200MHz or 400MHz & 1GHz, Don't be afraid of lowering that HTT Multi.

deeppow · May 28, 2005

Glad to see ya back altec. :welcome:

But then I've not been around a lot myself. One of these days I may even get 7 stars,....maybe.

The A64 names really threw me when I decided to change. Names for speed, bus, and technology are all the same, HTT, sometimes. And then again two different web sites may use the names differently and you'll frequently see FSB used and sometimes interchanged with HTT. I finally decided they must have let the marketing folks name everything since it made no sense to me the scientist.

After spending a reasonable amount of time, I think I finally "grok" the A64 names most of the time. And even if the names are confusing, I can overclock. I did expand my guide to include the A64 but I'm still testing to validate much of the variations that are now available.

calcal · May 29, 2005

amd clock higher cuz of lower multipliers???

Gautam · May 29, 2005

You get a little more flexibility in terms of running the memory faster, yes, by having the multiplier downward-unlocked.

deeppow · May 29, 2005

Ya, the cpu multiplier effect is really no different than the XP.

My picture of a quick understanding is as follows:

1) Memory and CPU behavior -- Running a memory ratio of 1:1, all you know about an XP applies to memory and CPU settings on an A64. It is when you use a different lower memory ratio that rounding of the memory dividers occurs that things get a little more complex.

2) XP has one bus called the FSB with communication to memory and perpherials.

A64 has two buses, a memory bus controlled by the CPU through its memory controller to communicate with the memory and a "HTT" bus that communicates with the perpherials.

You control the two A64 buses separately.

Anyway, I learn better with pictures. Others with words. My 0.02 cents.

CJ4 · May 31, 2005

This may help:
http://www.xtremesystems.org/forums/showthread.php?t=61939&page=1&pp=25

CJ

zer0nix · Jun 1, 2005

LoneWolf121188 said:
CPU speed/RAM divider=RAM speed
And thats about it!

shouldn't that be "cpu speed X ram divider = ram speed"?

altec · Jun 4, 2005

Gautam said:
Hey welcome back bro!

If we're strictly talking speeds, you could look at the HTT as if it were the FSB..

HTT x CPU multiplier = CPU speed, i.e. 9x200=1800, 200 is the HTT speed.

The main difference between the FSB and the HTT is that the HTT doesn't actually carry any data; its just a number.

The memory speed is then derived off the CPU speed, at 1800MHz you could have 180MHz with a CPU/10 divider, 200 with a CPU/9 divider, 164MHz with a CPU/11 or 225MHz with CPU/12 for instance.

That's whats really important. The HyperTransport bus is analogous to the FSB, sort of, but you don't usually have to worry much about it.

Ok, ok that makes a little more sense, but what you are saying is that the HTT isn't really a bus at all, but just a number to determine CPU speed...
Won't that complicate the whole process a bit more though since this way you have to monitor the stability of two busses? If you do run into instability problems, are'nt they a little harder to identify quickly?

deepow said:
Ya, the cpu multiplier effect is really no different than the XP.

My picture of a quick understanding is as follows:

1) Memory and CPU behavior -- Running a memory ratio of 1:1, all you know about an XP applies to memory and CPU settings on an A64. It is when you use a different lower memory ratio that rounding of the memory dividers occurs that things get a little more complex.

2) XP has one bus called the FSB with communication to memory and perpherials.

A64 has two buses, a memory bus controlled by the CPU through its memory controller to communicate with the memory and a "HTT" bus that communicates with the perpherials.

You control the two A64 buses separately.

Anyway, I learn better with pictures. Others with words. My 0.02 cents.

The pictures definatley helped a bit, but if the memory bus is completely controlled by the CPU, and there is no FSB, is the only ceiling in memory speed the physical chips?

If so, what are consistantly producing the best results?

Thanks for the welcome back fellas, I need to get back into this stuff, and I finally have soe free time again for the stuff I enjoy.

altec · Jun 4, 2005

BTW Gautam, congrats on the blues.....

deeppow · Jun 4, 2005

I've ended up throwing away the names FSB and HTT because they confuse more than anything else; I just call it the clock speed. Works better for both the XP and A64 setups. In the old days FSB was used more to denote speed than the bus characteristic anyway.

altec said:
if the memory bus is completely controlled by the CPU, and there is no FSB, is the only ceiling in memory speed the physical chips?

Yes you got it, you are physically limited by the memory chips which are getting better of course.

Turns out the highest you can get the memory speed is the clock speed --- same as before. With the mem ratio at 1:1 (and not using the 1/2 cpu_mult), your cpu_mult=mem_divider so that memory_speed=clock_speed. Same game you've played before.

The advantage is you see a gain in memory performance from going through the CPU because the memory latency is decrease. Memory data has its own bus, not sharing like it was when only the FSB existed.

Been a while.....

altec

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