OCing multiplier-locked AMDs

T

TrainTrackHack

VIP Member
Okay, so someone in these forums asked that what's the point of having multiplier-unlocked CPUs, when you can OC by raising the FSB. And then someone replied that raising the FSB too much can cause unstability and you need a nortbridge cooler cabale of dealing with the heat. But since AMD boards don't have FSB or northbridge, does this apply to them? Is there any point buying multiplier-unlocked AMDs, unless you're very very VERY serious overclocker?
 
AMD motherboards do have a northbridge, they use something called HTT instead of FSB, but its basically the same principle when overclocking,
 
...but all FSB traffic goes thru the single northbridge chip, whereas HT is some kinda "point-to-point" thingy...it's not controlled by a single chip, is it?
 
AMD still uses a basic 200 bus speed that the northgbridge runs at. When you raise the bus speed up from 200mhz when overclocking it raises the Hypertransport and memory bus speed as well, really all the buses but most boards now have the PCI bus locked a 33.3mhz
 
I know, I know...let me rephrase my question:
Is there a limit on rising HT bus speed? Like m/b FSBs are rated 800,1066, 1333 and so on, going past those can cause instability/northbridge chip overheating...is there a "rating" on HT that limit the amount you can overclock? And back to the heat problem...for what I know, there's no single "HT chip" similar to n/bridge...if something apart from the CPU overheats as a result of OCing, what is it gonna be then?
 
Ok, the Hypertransport speed on a Athlon 64 939 or AM2 is 1000/2000, that is X5 of the 200 mhz bus speed. The hypertransport limit on stability is somewhere between 1050 and 1075mhz maybe more depending on the quality of the board, but having a higher or slower HT speed to a point has not effect on performance. So if your raise you bus speed to oveclock, your HT speed increases 5 mhz for every 1 mhz you raise the bus. When your HT gets near the instability point you just set the HT mulitplier to X4 and it lowers your HT speed back down. As far as heat when raising your bus speed from 200 mhz does raise the heat of the northbridge by a small amount but you really only have to worry about heat when you raise the bus speed up enough to cause the northbridge to go unstable and you bump up the voltage to get it stable. Voltage is the devil of heat not mhz speed. Raising voltage to get stability is what really starts the heat buildup when overclocking.
 
So, if I got this right...raising HT doesn't affect CPU speed, it's rasing the bus that does so...both HT and CPU run to the beat of the bus, and you can set multipliers of both CPU *and* HT separately?
 
Like taylormsj said that is more or less correct. The Hypertransport and CPU have separate multipliers. Raising the basic bus speed increases both but you can drop the HT multiplier to get it back in spec.
 
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