Advantage of lowering multiplier?

[Guest]

Was wondering why "unlocking" the T-birds & XPs is all that necessary for OCing, when most (or all) big gains can be made by simply raising the FSB speed? I know that some folks OC by raising the multiplier and others by combining raised multiplier & FSB settings, but others still speak of getting the best maximum tweak by lowering the multiplier & trying different FSB combos.

Example: I have a T-bird 1.33/133(266). I can, and have, effectively raise my CPUs frequency to 1.6g by leaving the mult. at 10x & cranking the FSB speed to 160. What's the advantage of lowering the mult. to 9.5 & raising the FSB even higher to reach the same speed? Am I missing something? Could I actually tweak it up even higher by lowering the mult?
(By the way, to several of you out there with posts on "unlocking" & OCing older T-birds or Durons, make sure your L1 bridges are cut. I had the pencil out & sharpened before I took a look at my 1.33 chip & bios and realized my multipliers can be changed w/out any mod.)

One more thing (for those posting they're having probs getting their T-birds OCed past one or two notches) upgrading to a new, high-performance MB is crucial. I had an older, AMD 760 (one of the first DDR) MB on which I could barely get my 1.33 to 1.35. I recently bought an ABIT KR7A-R MB and the same old T-bird runs rock solid at 1.6, even at max memory settings. The additional OCing features (i/o- DDR- core voltage, mult. settings, etc.) obviously help, but the hardware & new chipset is vastly improved for OC support.

Sorry to get off the subject of my original inquiry, but I thought I'd kill 2 birds & offer that for some recent posts I've read. OK, OC gurus... what's the real deal w/ multiplier lowering? Thanks for any/all info.

 

[girish]

Well, there are two methods to overclock the processor, eiter increase the FSB or increase the multiplier. To change the multiplier on AMD processors it needs to be unlocked. Intel processors have a permenantly locked multiplier so all we can do is to increase the FSB.

Now, assuming you have unlocked the multiplier many people will recommend you to lower the multiplier and go for higher FSB. Thats perfectly practical.

Basically, with every MHz you increase on the FSB, the core speed of the processor increases by the (multiplier) number of MHz, i.e. for a Athlon 1 GHz with a multiplier of 10, every increment in the FSB increases the core speed by 10 MHz. While all this is fine, you need still finer settings when you approach the max speed. Most of the times, higher core speeds can render the system unstable, but at the same time the memory speeds have some potential to work overclocked. In such cases, even if you cannot get the processor work faster but the memory can work faster, you can lower the multiplier so that you get core speeds near about the rated but a faster memory subsystem. That helps improve the performance even while the processor is still running at its rated or slightly overclocked speed.

Thats the difference between a Athlon 1000(100x10) and Athlon 1000(133x7.5)! You have a play of half the FSB with a single multiplier step.

girish

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[camieabz]

The reason you increase the FSB, is so the motherboard, RAM, cache, AGP & PCI buses all run faster, improving overall performance. Sometimes increasing these factors can be harmful to hardware though, so use parts which can take it.

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[Guest]

Thanks, girish. I guess I understand how lowering the mult. could get you that extra one or two clicks when you're reaching the threshold. You're point on cranking up the memory bus while leaving the CPU core speed down also makes sense. Good info.

btw- camieabz, thanks for the effort, but I understand what raising the fsb does... i was wondering about multiplier lowering.

 

[Unolocogringo]

what camieabz was trying to say I think . Is if yuor processor will only do 1000 you are better off at 7.5x133 than you are at 10x100. The higher fsb usually means the memory ia also running at 133. Making it faster.
Now we get to a point when some part can't handle the fsb speed and crashes.
First set your memory to it's fastest settings. Now overclock until you reach your systems best running setting.
I can run my system at 158 fsb with memory at 2/2/2/7/9. 133/133/33.
I can also run at 174fsb ,memory at 3/2/2/7/9, 133/100/33.
Believe it or not the 158 fsb wins in all benchmarks.
This is on a P3 so I cant change the multiplyer.

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[Guest]

Thanks, Rick. That also agrees w/ what girish said about lowering the mult. & raising the FSB for faster memory (and other devices on the bus, if they can take it).

I also have similar experiences (to yours) w/ jacking up my memory settings & how performance compares w/ high fsb overclocking. I can max all my memory settings at default cpu speed and get almost identical benchmarks as default memory settings w/ my fsb from 133 to 150.

btw, what order are you listing your mem settings? I thought latency, interleave, trp, tras, trcd... (the order in my bios) but those numbers don't add up. And is the 2nd set your timing ratio?

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[Unolocogringo]

On my cusl2-c you can choose fsb/mem/pci or 133/133/33 or 133/100/33 so that you can run your memory at 100 while your fsb is at 133 with the pci at 33.
the other numbers are memory timings themselves. 2/2/2/5/7, 2/2/2/7/9,3/2/2/5/9,3/3/3/5/7 or 3/3/3/7/9. Of course the lower the number the lower the wait states.

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[Guest]

im still tryin to grasp what exactly the numbers represent in ur memory timing? does it correspond to the order of things as dman708 stated (ie: latency, interleave, trp, tras, trcd... ) thanx