Modded ASUS P5Q/Pro/Deluxe/Premium BIOS

[DMF]

Googled a thread right here on the forum. I've done a little editing to make it clearer:

Your north bridge has an internal clock speed and latencies just like your CPU and memory. The FSB of your north bridge can be found by dividing your original CPU multiplier by your set CPU multiplier and then multiplying by your set FSB.

So if you are running a E6600 (2.4 GHz or 266 * 9) at 3.2GHz (400 x 8) your NB FSB is:

(9 / 8) x 400 = 450Mhz FSB (1800Mhz Total)

Just like your memory may be able to run at 4-4-4-12 at 1000Mhz but needs to run at 5-5-5-15 at 1200Mhz, your north bridge has a series of latencies which it must adjust in order to maintain stability at its FSB. These latencies seem to play a far more significant role in system performance than memory latencies. - emphasis mine

Intel has predefined specific latencies at specific NB FSB speeds. They are referred to as straps. There is a strap for when the NB FSB is 1066Mhz and under, 1333Mhz FSB and under, 1600Mhz FSB and under, etc. When you go from the 1066Mhz FSB strap to the 1333Mhz FSB strap, the north bridge's internal latencies loosen to allow for greater stability.

ASUS has redefined the NB strap so that the 1333Mhz FSB strap does not come into effect until 401Mhz FSB (1604Mhz). Other perimeters of straps are someone unknown.

Ponder this table from farther down in the thread. Note that ref freq (reference frequency) is another name for 'FSB Strap to NB'.

I haven't quite figured out the relationship between ref freq, mem freq, and ram speed. mem freq is the value selected for the 'DRAM Frequency' setting. Note that in all cases the CPU frequency is constant.