Please explain 'CPU/Memory Frequency Ratio' to me...

[Fun Guy]

I have three setting in the BIOS of my Asus P4B533-VM:

- Auto
- 1:1
- 4:3

Can someone explain to me what these mean and how significant they are?

 

[chizow]

Originally posted by: Fun Guy
I have three setting in the BIOS of my Asus P4B533-VM:

- Auto
- 1:1
- 4:3

Can someone explain to me what these mean and how significant they are?

Its the relationship of your memory speed to your front side bus speed. Its a relatively new option on motherboards that allow people greater flexibility in performance according to memory quality (I think its just there for OCers though ). Basically, Auto means your memory will run at whatever frequency the dimms are programmed/rated at, so PC2100 runs at 133mhz FSB, PC 2700 runs at 166mhz...etc. 1:1 means your memory and FSB are "synced" which means they are running the same frequency, ie 133/133, 166/166. 4:3 would be like 133/100 or some variation of the same ratio. When memory and the FSB aren't synced you get into latency issues. At some point, latency can actually diminish system performance, so any benefits of running your memory at a higher frequency is lost.

Chiz

 

[Viper96720]

To find out your memory speed take your fsb speed and multiply it by the divided ratio. A fsb of 133 with the 4:3 ratio would be 133x1.33333333333333333333 since 4/3=1.333333 then your memory would be running at 177mhz. You would use the 4:3 if you had a 100mhz cpu and wanted to run the memory at 133mhz. If you had a 133mhz fsb cpu and 133mhz memory you use the 1:1 ratio. The memory speeds are multiplied x2 for ddr speeds.
For any ratio just divide it and multiply by the fsb speed to get the memory speed.