Ram divider confusion

[carholmes]

I just got a new 3700 sandie and while I was messing around with settings I noticed that there was some inaccurate readings on cpu-z. I had my system set at 275x11 and ram divider at 9/10 and cpu-z reads 252.2 with a ram divider of 12. ]11x10/9[ is 13 right, and 3025/13 is 232.69. I even double checked with A64 MemFreq 1.1. Could it be something wrong with the bios? Or is it something else?

[cuoficr]

Actually thats 100% right. 275x11 = 252mhz when using the 180 divider.

 

You calculate an A64 memory divider like this:

 

CPU multiplier * Divider = Memory divider, Then CPU speed / Memory Divider = Memory speed.

 

Your example:

 

275 x 11 = 3025 CPU speed.

 

So... 11 x 12 / 11 (180 divider is actually 11/12 not 9/10 as listed in the bios) = 12 for memory divider.

 

3025 / 12 = 252 ram speed.

[carholmes]

Now I'm even more confused. When i first came across this prob i out right calculated it wrong and someone refered me to the section in the Definitive DFI AMD OCing guide and it said

How to calculate your memory frequency

 

Memory Frequency = (FSB x (CPU ratio)) / ] ((CPU ratio) x (FSB : DRAM ratio)) [

 

Ceiling function is shown with ][,

eg

]10.1[ = 11

]10.2[ = 11

]-6.2[ = -6

]-8.9[ = -8

 

For positive numbers always round up to the nearest whole number.

For negative numbers always round down (its actually still up) to the nearest whole number.

 

Big example

FSB = 290

CPU ratio = 7

DRAM:FSB ratio = 5:6, re-arrange to 6:5 (FSB : DRAM)

 

Using the formula,

Memory Frequency = (FSB x (CPU ratio)) / ] ((CPU rato) x (FSB : DRAM ratio)) [

 

Memory Frequency = (290 x (7)) / ] ((7) x (6/5)) [

 

Work this bit out first

] ((7) x (6/5)) [

 

6/5 = 1.2

 

and that becomes

] (7) x (1.2) [

 

7 x 1.2 = 8.4

 

Now remember the ceiling function, ][

 

]8.4[ = 9

 

Put that back into the main formula

 

Memory Frequency = (290 x (7)) / 9

 

So

Memory Frequency = (290 x 7) / 9

= 225.5Mhz.

It also recomended using an app that calculates the above formula for you , called A64 MemFreq 1.1 So I guess the guide is wrong.

[carholmes]

Oh wait I'm an idiot I just noticed the part in your post where is says that the 9/10divider is acually 11/12. So the guide isnt wrong just left out the part about the 9/10 divider. my bad

[carholmes]

Soory for the triple post but, cuoficr do you know of any other dividers with secret identities?

[cuoficr]

I only know about that one because it was before the new version of CPU-Z and i was having the exact opposite of your problem CPU-z was reporting a mem speed of 232, so I posted on TBE and got the answer from OCZ Tony.

 

TBH The whole deal of dividers still somewhat confuses me, particulally how CPU Multiplier's affect it. (292x12 on a 180 divider also equal's 250mhz RAM speed for example). I have'nt really studied it to in depth, except for finding out what I needed to do with my own chip's. Basically anything to do with the 11x multiplier and A64 info's calculator, or any other calculator I've come acrss is wrong is wrong at this time.

[carholmes]

The reason why two different fsb values can yield the same mem freq is because of the ceiling function in the calculation.