time said:
Oh yes, I'm also running with all three DIMM slots populated with Transcend/Samsung PC3200, currently at 221MHz.
Actually Time, your mem speed is 217. A number of apps incorrectly calculate the mem speed when using memory ratios. Allow me to demonstrate:
First off, the correct determination of memory frequency when employing a memory divider on the A64 is given by:
Code:
Mem Frequency = CPU clock speed / mem divider
= (HTT x CPU multipler) / ceiling[ceiling(CPU multiplier) x "base HTT:mem ratio"]
The cpu clock speed is obviously straight forward.
On the otherhand, the way the A64 mem controller calculates the memory divider is not as straight forward. First thing to note is that the memory divider has to be an integer, which is accomplished by the first ceiling function. The second, and perhaps even more interesting feature to note, is that the inner ceiling function insures all fractional CPU multiplers are rounded up to an integer value. The negative ramifications of this effect will be illustrated by example to follow. Third, the ratio (in the memory divider side of the equation) is actually the inverse of the "mem:base HTT" ratio in the BIOS. For example, if one sets a 5:6 (in otherwords 166:200) ratio in the BIOS, a corresponding ratio of 6:5 is used in determination of the memroy divider.
Now, taking your example, we have a HTT=266, CPU Multiplier=9, and a base HTT:memory ratio of 6:5 (although you didn't devulge this, it is, by deduction the only possibility). Thus, your:
memory frequency = (266 x 9) / ceiling[ceiling(9) x 6/5]
= 2394 / ceiling[9 x 6/5]
= 2394 / ceiling [10.8]
= 2394 / 11
= ~217
Apps that do not calculate the speed correctly do not use the ceiling fn. For example:
memory frequency = (266 x 9) / (9 x 6/5]
= 2394 / 10.8
= ~221
Now, about that half multiplier example, how about we use your values again but with the exception of using a 9.5 CPU Multiplier:
memory frequency = (266 x 9.5) / ceiling[ceiling(9.5) x 6/5]
= 2527 / ceiling[10 x 6 /5]
= 2527 / 12
= ~210
Shocking isn't it!
Just to give a final example, suppose CPU Multiplier = 8.5, HTT=240 and the BIOSes "Mem:HTT" ratio is 5:6, then:
Mem speed = (240 x 8.5) / (ceiling[ceiling[8.5] x 6/5])
= 2040 / ceiling[9x 6/5]
= 2040 / ceiling[10.8]
= 2040 / 11
= 185MHz
If you work the last one through but use a lower 8x CPU multiplier, you will observe that memory gets driven at 192.