Quote Originally Posted by gtj View Post
I need to add some descriptive text to that calculator.

Facts:

The terms Front-Side Bus and Host Bus are synonymous.

The FSB between the CPU and MCH is quad-data-rate and 8 bytes wide. That means that data passes at 4 times the frequency and it's 8 bytes per clock. I.E. If the FSB Freq is set to 266 then the actual data rate is 1066 MHz (the advertized FSB) or 8528 MB/s (266 * 4 * 8).

The MCH has internal timings just like your memory. The only control you have over those timings is by setting the Reference Frequency which tells the MCH what frequency to ASSUME it's running (strap), not what it will actually be running at as set by the FSB. The MCH then sets it's internal timings accordingly. The higher the strap, the looser the timings will be based on the assumption that the higher the frequency, the looser timings will be required to be stable.

Both the FSB and Reference frequencies are set using their BASE frequencies not the QDR equivalent. I.E. 266 not 1066. It may be REPORTED as the QDR equivalent on the main BIOS page.

The Memory Bus between the MCH and the memory is dual-data-rate and 8 bytes wide. The actual frequency is controlled by the FSB frequency and the ratio of Ref Freq to Mem Freq. To make things a little more confusing, the Memory Frequency is set using the DDR equivalent not the base frequency. Hence 266/533 is 1.0 or 1:1 ratio. So if your FSB is set to 266 and your ratio is 1:1 then your memory will be running at 266MHZ or DDR2-533 and the throughput will be 4264 MB/s (266 * 2 * 8).

If you put DDR2-800 memory in the board, it will default the reference and memory frequency to 266/800 and the FSB to 266. If you do the math, you'll see that this makes the memory run at it's DDR2-800 rated speed. You'll also notice that with a 2/3 ratio, your memory is running 33% faster than the FSB which could be a waste.

My Conclusions:

The 266/1033 strap (Reference Frequency) is optimal. Unless you plan on running a FSB of 450 or higher, going higher on the strap will unnecessarily loosen the MCH timings. You probably won't even be able to boot on a strap of 200 or 133 unless you underclock.

A 1:1 ratio is nice BUT watch the effective throughput of both the FSB and Memory. Ideally, you want the Memory throughput to be slightly higher than the FSB throughput. If you do very heavy disk IO, then the memory thoughput could be even a little higher to allow for direct access to the memory from the disk controller (DMA). Balance this with the speed, latency and voltage capabilities of your memory.
Boy that's going to take a while to digest. That is just way over my head lol. Anyways I turned it down to 9x320 just to be safe until I get a proper aftermarket cooler. The memory I left at 533 4-4-4-12 @ 2.12v. That is 1:1 on the 1066 strap right? Sound good?