CPU-Z reporting memory frequency incorrectly?

[warbean]

Hey all,

I have my 3800+ Venice running at 11 x 243FSB for 2.67ghz.
I am running Corsair XMS DDR400 so wanted to keep my memory frequency around 200 to be stable and have tight timings, so I am using the 166 divider.

According to my math, that leaves memroy frequency at 243 x .83 = 201.6mhz, perfect. BIOS confirms my DDR clock to be there as well, but CPU-Z says my frequency is 190.9mhz, a 5% discrepancy. It says my FSBRAM ratio is CPU/14, or 2670/14=192. Where are they getting that ratio? Is my math wrong?

First time OCing using a divider, so I may well have screwed up somewhere....

 

[996GT2]

I wouldn't worry about a little difference like that, as long as your RAM is under 225 or so you're ok. There's going to be like a 1% performance difference from a slightly higher RAM speed anyway, so don't sweat it.

 

[SynthDude2001]

200*11/166=13.25, which gets rounded up to 14. That's your actual memory divider (divided down from the CPU speed). So ~191MHz is correct for your effective RAM speed.

The divider you choose in the BIOS (133, 166, etc.) does not work as an actual ratio against your FSB(HTT) speed unless you're using a 10x multiplier. Took me a while to grasp it too after I came from an Athlon XP, but that's the strange way that RAM divider math works on the A64. It is annoying that you can't get more precise RAM speeds (I can't get my RAM right around 200MHz with my overclock either), but it is what it is.

 

[warbean]

Originally posted by: SynthDude2001
200*11/166=13.25, which gets rounded up to 14. That's your actual memory divider (divided down from the CPU speed). So ~191MHz is correct for your effective RAM speed.

The divider you choose in the BIOS (133, 166, etc.) does not work as an actual ratio against your FSB(HTT) speed unless you're using a 10x multiplier. Took me a while to grasp it too after I came from an Athlon XP, but that's the strange way that RAM divider math works on the A64. It is annoying that you can't get more precise RAM speeds (I can't get my RAM right around 200MHz with my overclock either), but it is what it is.

This is exactly what I wanted to know- thanks so much.