To truly understand the formula of RAM speed for a A64, one must first understand how the A64 system arcitechure works. All data travels through the "Hyper Transport Tunnel", which is really fast, 800 or 1000MHz, and can carry 20GB/s data.
There are a lot of "clocks" in the A64 system, most of which operate independent of each other. There is the system clock, which is where the CPU gets its Speed from, where the AGP and PCI get theirpeed from in unlocked systems, and the Hyper Transport Tunnel gets its total speed from This is commonly called the HTT.
In most systems, however, the system clock only controlls the speed of the CPU and the Hyper Transport Tunnel, since the PCI/AGP and PCIe are all locked at their own optimal frequency.
The term FSB for A64's is a misnomer. RAM speed is linked to CPU speed. The computer derives CPU speed from the system clock and its internal multiplier, most commonly from 8 to 14x in current systems, though most BIOSes support up to 25x. RAM speed is derived by dividing CPU speed by the dividend of the CPU multiplier and the RAM divider.
Matmatically, this is shown by the function R= C/(M/[D]), where C is CPU speed, D is the RAM divider (normally either 1 or a fraction), M is CPU multiplier, and R is RAM speed.
For .5x multipliers, To get your RAM speed, you must round your CPU multiplier UP. AMD did this for stability reasons, as rounding down would have increased RAM speed, and therefore the chance for system instabilty.
Example: A clawhammer 3200+ runs stock 10x200. You overclock it to 10x240, but your ram can't run 240MHz, so you run it with a 166MHz, or .83 divider. 2400/(10/[.83]) gives you exactly 200MHz.
This formula, combined with the Hyper Transport Tunnel, also explains why A64's exhibit no performance degradtion when running ram dividers. To use my previous example, 240x10 with a 166MHz RAM divider looks exactly the same a 12x200 to the computer.
I hope this little guide helps anwswer some questions people have, because it doesn't explain just what, but why. Explaining why something happens helps people find their own answers, and come up with new ones.
