Memory Speed Not As Expected

[nheather]

I just built a system using

Athlon64 3700+ (SD)
Asus AN8-E
2GB (2 x 1GB) Geil Value RAM

I am successfully overclocking as follows

FSB = 250
Multiplier = x11
CPU Speed = 2.750GHz
HTT Multiplier = x4
Memory Freq Setting = 333MHz
Memory Timing 2.5-3-3-7 at 1T

All very good, but my question is about the memory speed. I expected this

I've set the memory speed to 333Mhz which I assume will impose a 1.2048 divider based on 400/333 or 200/166.

But as the FSB is running at 250 rather than 200 I expect the actual memory speed to 250/1.2048 = 208MHz.

If I look at A64Tweaker it just shows the memory as 166MHz - I assume it is just reading straight from the BIOS.

However, if I use CPU-Z it's more like I expected - it shows 196MHz.

But its not 208MHz!

If CPU-Z is correct, I'm losing 12MHz on the RAM speed.

Does anyone know why this could be???

BTW the CPU speed shows exactly as expected at 2.750GHz.

Cheers,

Nigel

 

[nheather]

Okay, done some reading on another forum and I have the answer - though it's a little disappointing.

The 166/333 divider actually varies depending on the CPU multiplier. nominally it should be 5:6 but for a CPU multiplier of 11 it is actually 11:14.

Using this multiplier gives the 196MHz as reported by CPU-Z.

This is disappointing because my RAM is actually running a little under speed and options seem limited.

Option1 - Run RAM at 1:1
I doubt very much my RAM could run at 250MHz (I guess 235 will be about the best), so this would limit the CPU overclock to 2.585GHz which is a shame because it could do a lot better.

Option 2 - Set CPU Multiplier to x10
I could run the CPU at 270x10 = 2.7GHz (again below what the CPU can do). The RAM would run at 212MHz. The HyperThread would have to be set at x3 so would run at 810 which is probably too low. Can't go any higher because I suspect that 270 is about the limit of the MoBo.

I can't think of anything else to do. I suppose I'm getting a good overclock with the CPU but I am disappointed with the memory. The Geil Value RAM seems a mistake - overkill for what it is doing but not good enough to keep up with the CPU.

Cheers,

Nigel

 

[Joe42]

I haven't read all that but on my A8n32 sli deluxe i found the memory goes up by half of what the fsb has been raised by.

So raise the fsb to 250 and memory ends up at 225. If you have the memory on a 166 divider, then its 166 + 25.

Hope thats some help.

 

[nheather]

Joe,

Perhaps that is an extra feature for the deluxe version.

The divider used for 166 depends on the CPU multiplier - it gets as close as it can get to 333/400 using whole number ratios. For example

CPU multi = x11 then divider is 11:14
CPU multi = x10 then divider is 10:12

So if you have a x11 CPU running at 250 with the 166(333) divider set then the memory runs at 250x11/14 = 196

It sounds like you board either has a 180 divider (which are rare) or an additional function to put an offset on the RAM speed on top of what is calculated by the divider.

I can't see any such function in my BIOS - would be really nice though.

Cheers,

Nigel