AMD Athlon overclocking

19 Sep 2007 19:03

I posted this for theonejrs some time back when he was playing with an Athlon 3700 and wanted to know more about overclocking AMD Athlon cpu's.Thought I would post it here as a reference for anybody who is thinking of doing the same.Remember this is for the Athlon 3700 which has a default FSB multiplier of 11.If your cpu is default @ 10x multi or 12x multi or higher,just change the calculations accordingly.

Ok,the default multi for the cpu is 11x200mhz=2200mhz.
Drop the multi to 10 and your at 2000mhz.
Drop it to 9 and your at 1800mhz......etc.Thats easy.
Your HTT(or fsb,same thing) speed is @ default 2000mhz(this is the speed the memory communicates with the memory controller).
If your memory is @ 1 to 1 with the bus speed(200mhz),your memory will be running at 200mhz as well,but the memory is double data rate(DDR)so we multiply that by 2 giving you 400mhz(DDR400).
The LDT/FSB multiplier works like this:
The default multi here is 5x.So LDTxFSB=5x200mhz=1000mhz.Thats one way.The memory is DDR so multiply that by 2 gives you 2000mhz.
Now say you increase your bus speed to 220mhz.Now we have 11x220=2420mhz effective cpu speed.But remember your memory runs in sync with the bus speed so now your memory will be running at DDR440(220x2).Your HTT(or fsb)will also increase to 2200mhz(220x5x2)so you can see the fsb is now overclocked by 200mhz.Thats not good for stability!!This is where the LDT/FSB multiplier comes in.Drop the LDT/FSB multiplier to 4x and you have 4x220x2=1760mhz fsb.Thats acceptible.Your memory will still be DDR440 because remember it's in sync with your bus speed which is still 220mhz.Raise the bus speed to 230mhz and you have the cpu at 2520mhz(11x230)your FSB will be at 1840mhz(230x4x2)and the memory will be at DDR460(230x2).
So now your memory is starting to speed up it may become unstable so we need to slow it down.This is where the DRAM/FSB ratio comes in.
Ok,the memory is at 460mhz(230x2) so lets say we put it on a 9/10 divider.
This is how to work it out:230 divided by 10 =23.Multiply 23x9 gives you 207mhz x2(DDR memory)=DDR414,thats better!Should run ok at that speed.If it doesn't,lower the divider again.

Actually overclocking and getting the settings at an optimal level takes some time(and frustration!) but hopefully this gives a clearer understanding how everything works.

Regards Crowy

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