A64 AM2 ram frequency equation?

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piako

[H]ard|Gawd
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Apr 5, 2006
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There used to be a great guide at
Code: 
http://forums.amd.com/index.php?showtopic=67749
but it doesn't work any more.

I know the "Bus Speed" x "Multiplier" = "Core Speed" and that you can set the "HT Link" multiplier lower so it doesn't get over 1000, but how is the memory frequency generated? I'm aware of the ram divider but am uncertain how the final ram frequency is calculated. The guide I posted used to explain but.
 
piako said:
There used to be a great guide at
Code: 
http://forums.amd.com/index.php?showtopic=67749
but it doesn't work any more.

I know the "Bus Speed" x "Multiplier" = "Core Speed" and that you can set the "HT Link" multiplier lower so it doesn't get over 1000, but how is the memory frequency generated? I'm aware of the ram divider but am uncertain how the final ram frequency is calculated. The guide I posted used to explain but.
Click to expand...

The memory frequency is generated by dividing the cpu speed by the memory divider and every cpu is different. For example, for the x2 3600 brisbane, the default speed is 200x9.5=1900mhz. For the 400 divider, you take the 1900mhz and divide it by the highest whole number that yields 200mhz or less. So then the largest number to divide into 1900 and get the closest to 200mhz is 10. Therefore, on an x2 3600 brisbane, the 400 ram divider is a cpu/10. So if you overclocked your cpu to 2500mhz, the ram would run at 250mhz (500 effective) with the 400 divider. The 533 divider yields cpu/7. Get it?
 
i arise from the dead.
to put birdie's explaination into a bit more concise form...



memory speed is set by cpu/x
x = ceiling ( cpu multi / memory ratio )
cpu is the cpu clock speed

so if you set the 400mhz memory ratio, which is 2:1, and an 11x cpu multi, and 250mhz htt speed...

cpu speed is 2750mhz
x = ceiling ( 11 / (2/1) ) = ceiling( 5.5) = 6

2750/6 = 458.33mhz



or another example... 333mhz ratio is 5:3, 9x cpu multi and 333mhz htt speed

cpu is 3000mhz
x = ceiling ( 9 / (5/3) ) = ceiling(5.4) = 6

3000/6 = 500mhz


further explaination in sig if needed
 
ok thx I see. so my mobo has available:
"DDR2 400" which cpuz calls "CPU/12"
"DDR2 533" = CPU/9
"DDR2 667" = CPU/8
"DDR2 800" = CPU/6

Are there mobos with better memory oc options? I only have four choices so. Basically to OC the ram any more I would have to fudge with the cpu multiplier and bus I guess. This deserves a spreadsheet some time.
 
AM2multisCPU.jpg


:D this might help:D
 
piako said:
ok thx I see. so my mobo has available:
"DDR2 400" which cpuz calls "CPU/12"
"DDR2 533" = CPU/9
"DDR2 667" = CPU/8
"DDR2 800" = CPU/6

Are there mobos with better memory oc options? I only have four choices so. Basically to OC the ram any more I would have to fudge with the cpu multiplier and bus I guess. This deserves a spreadsheet some time.
Click to expand...

just remember that the memory divider that each ratio gives changes with the cpu multi. from what you say, i assume you are using the 12x multi :D

and afaik, those are the only 4 ratios the current AM2 chips support. it seems that K10 should give ddr2-1066 support.. or 8:3, and i would assume a 7:3 ratio as well just to make things flow better ;)
 
^ cool thx. I bought some new DDR2-1066. this one. I also made a giant spreadsheet so to figure it out. I think with my proc I'll shoot for 10x260 which will put the ram at 1040(520) MHz (CPU/5) and the CPU at 2600 MHz (stock 2400) so 200+. Thx for confirming that eclipse I didn't realize the divider changed w/ the cpu multp. :D :D :)
 
SS :) easy to use. shows ram, cpu frequency, lets you record you FSB clocks max-out plus your oc session.
 
Ok fellas you heard it from the Man DO NOT USE Calculator for exact clocking. Only use to get a idea how overclocking worksDidnt know wasnt accurate..:mad: .But it does give you a lil notion how Overclocking works though.:D

thanxs for the Warning ECLIPSE i didnt know:eek:
 
Why is the calculator wrong?

Try these numbers:

FSB=250
CPU multi=11
CPU speed=2750
RAM divider=166mhz ( 5:6 )

using Eclipse's formula:

2750 / ( 11 / [5/6] ) = 2750 / 13.2 = 208, which is what that page gives.

Then again, I am a newb at this.
 
For 11x250=2750 the correct ram frequency calculations are:
ddr2-400 = 611 MHz
ddr2-533 = 786 MHz
ddr2-667 = 917 MHz
ddr2-800 = 1100 MHz

see post #11
 
Tanatz said:
Why is the calculator wrong?

Try these numbers:

FSB=250
CPU multi=11
CPU speed=2750
RAM divider=166mhz ( 5:6 )

using Eclipse's formula:

2750 / ( 11 / [5/6] ) = 2750 / 13.2 = 208, which is what that page gives.

Then again, I am a newb at this.
Click to expand...

you left out the ceiling function. it's 2750/14, not /13.2, since the memory dividers only come in integers ;)
 
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