The relationship between CPU Multiplier & Memory Speed on AM2 processor
Bluetooth 26 May 2006

The chart

So, what we did was setting the CPU to 9x and CLK to 300MHz. RAM is set to DDR2-800, CAS 5-5-5-10,2T. The system booted up. Sandra 2007 was run and the score was barely higher than the previous score in the earlier screen shot. The CPU:MEM ratio is 2x when CPU mutliplier is 10x e.g. if ram runs at 200MHz, DDR2 will be at 400MHz (DDR2-800). If ram runs at 300MHz, DDR2 will be at 600 (DDR2-1200).

The chart belows shows that on the AM2, it depends on what multiplier you use. For example, if you use 9x, setting your modules to run at DDR2-800 in BIOS, you will see that CPU-Z will show you 360MHz, which is in fact, DDR2-720, it downclocks the ram.

Just as I expected, we didn't see 600MHz for the ram, but a check using CPU-Z shows that the ram is in fact running at 540MHz or DDR2-1080 when we ran the CPU at 9 x 300MHZ.

Lets do the maths when CPU mutliplier is set to 9. When BIOS is set to DDR800, and cpu is run at 200MHz, you will get 360MHz (DDR2-720), that is to say the ratio is 200:360. Thus when we run the CPU at 300MHz, according to the chart, it should give us 540MHz which is correct.

So when you o/c your system next time and find your ram not running at the correct values using CPU-Z, you are not alone. You can refer to the chart below to do a simple calculation and find out what is your expected speed of your DDR2 module running at.

It can also be observed that in order to run DDR2-1200, you would need to run 10x300, 12x300 or 14x300 or 16x300.. The rest of the multipliers will give you a value less than DDR2-1200 (or ram running at 600MHz).

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