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Can someone explain the maths of working out dividers?

post #1 of 11
Thread Starter 
Ok when i'm in Windows I usually use Gogars OC Optimizer to work out the correct divider to use, but sometimes in the BIOS i'd like to change it and be able to work out what my mem clock is actually going to be. But it never comes out the same as in the Optimizer?

For example if I was to work out a divider of 4:3 with a FSB of 200 here's how i'd do it:

200/3 = 66.6666* x 4 = 266.6666*

But gogars optimizer gives me 257.14???

So what am I doing wrong, is that not the right way to work out a divider ratio?

like always i'll rep+ whoever gives me a good answer as this has been wrecking my head for days and I can't find a decent explanation on dividers anywhere.
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post #2 of 11
Your divider calculation is correct. What values are you entering into the optimizer? It provides various possible OC settings based on each component's individual best OC.

Maybe due to this: http://math.gogar.com/athlon64.cgi?showtable=1 ?
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post #3 of 11
Thread Starter 
Yeah but the thing is CPUz reads teh RAM clock at the same value that Gogars Optimizer calculates it at?

The values i'm putting in to test are, these aren't my actual values:
CPU: 2800
RAM: 275
HT: 1050
FSB: 200
Multi: 9x

The first recommendation is what i'm talking about, how is it getting to that value?
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post #4 of 11
Quote:
Originally Posted by leimrod View Post
Yeah but the thing is CPUz reads teh RAM clock at the same value that Gogars Optimizer calculates it at?

The values i'm putting in to test are, these aren't my actual values:
CPU: 2800
RAM: 275
HT: 1050
FSB: 200
Multi: 9x

The first recommendation is what i'm talking about, how is it getting to that value?
that's weird, those numbers don't match up: multi * FSB = CPU frequency and 200 * 9 isn't 2800

what are your actual values?

EDIT: are you sure it's your real fsb you're looking at not the default? can I see a CPUz screenshot?
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post #5 of 11
Thread Starter 
Quote:
Originally Posted by SirJohnMichalot View Post
that's weird, those numbers don't match up: multi * FSB = CPU frequency and 200 * 9 isn't 2800

what are your actual values?

EDIT: are you sure it's your real fsb you're looking at not the default? can I see a CPUz screenshot?
??? no you don't understand how the calculator works. You put in you MAX possible values that you know of, and the calculator work out the best possible configuration which meets all of those limits. All of the values are seperate from each other, it is not calculating 200*9 = 2800, you are saying what is the best possible speed I can get out of a system if I know the CPU is capable of 2800, the FSB 200 and the multi 9.
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post #6 of 11
Your putting in that your max FSB is 200mhz?
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post #7 of 11
Thread Starter 
Quote:
Originally Posted by prosser13 View Post
Your putting in that your max FSB is 200mhz?


Ok... like you would of known if you'd actually read through this thread, these aren't my actual system limits, i'm just illustrating a set of values which will make the calculator give you a divider value. Again, if you read the title of this thread, i'm looking for an explanation of the maths needed to calculate dividers values, NOT what values I am using in my system presently.

Ok I think it would be more simply put if I say:

Say you had a FSB of 250Mhz, and divider values of 1:2, 2:3, 4:5

What should be the resultant memory clock values for each of these dividers?
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post #8 of 11
Ram dividers... a bit of a pain some times.
Multiplyer(ratio) = varable which may need rounding up or down unless it equals a whole integer. Then divide the varable into the CPU clock speed
That varable is the factor you seem to be missing.

Using a speculative CPU OC of 2500 even though it don't always work out to exactly 2500 due the multiplyer varables.
10(5/4)= 12.5 With a CPU @ 2500 or 250x10= CPU OC of 2500MHz, soif you rounded up the variable integer of 12.5 to 13 or 2500/13= 192MHz RAM bus speed
8(5/4)= 10, If the CPU speed was still 2500 (speculative) your RAM bus speed would be 250... or 2500/10=250
So what ever divider you use not only reduces the default speed starting point, it increases @ the ration to every 1 MHz the CPU is increased give or take due to the whole or rounding of the whole integer.
Whole integers are easier to relate. Set to DDR200 or 1/2 the CPU speed and for every 100MHz increase the CPU gains, the RAM increases 50MHz when using a 10x250 OC. 10(2/1)=20 so 2500/20= 125MHz
(Note the DDR200 example, even though the RAM is 1/2 the CPU speed, it illustrated you factor with a 2/1)
What is a PAIN is the intergers that are not whole.
Some odder workings with a 9 multiplyer... and continuing with the speculative CPU speed of 2500
9(5/4)= 11.25, In this case round down to 11 and 2500/11= 227

Hope I that right

    
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post #9 of 11
Quote:
Originally Posted by The Duke View Post
Ram dividers... a bit of a pain some times.
Multiplyer(ratio) = varable which may need rounding up or down unless it equals a whole integer. Then divide the varable into the CPU clock speed
That varable is the factor you seem to be missing.

Using a speculative CPU OC of 2500 even though it don't always work out to exactly 2500 due the multiplyer varables.
10(5/4)= 12.5 With a CPU @ 2500 or 250x10= CPU OC of 2500MHz, soif you rounded up the variable integer of 12.5 to 13 or 2500/13= 192MHz RAM bus speed
8(5/4)= 10, If the CPU speed was still 2500 (speculative) your RAM bus speed would be 250... or 2500/10=250
So what ever divider you use not only reduces the default speed starting point, it increases @ the ration to every 1 MHz the CPU is increased give or take due to the whole or rounding of the whole integer.
Whole integers are easier to relate. Set to DDR200 or 1/2 the CPU speed and for every 100MHz increase the CPU gains, the RAM increases 50MHz when using a 10x250 OC. 10(2/1)=20 so 2500/20= 125MHz
What is a PAIN is the intergers that are not whole.
Some odder workings with a 9 multiplyer... and continuing with the speculative CPU speed of 2500
9(5/4)= 11.25, In this case round down to 11 and 2500/11= 227

Hope I that right

Hi Duke.As always great explanation.
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post #10 of 11
That stuff will drive me crazy, wait, I am crazy
Just hope it explaned it correctly!
    
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