On Abit mobos, the FSB and memory ratio can be changed independently. The memory speed still changes with FSB, but the ratio will allow you to use 1:1 (both exactly the same) or you can run the RAM slower than the FSB with a ratio like 5:4 or 3:2. For example, if you are at 250 FSB and your PC3200 RAM can't handle that speed at 1:1, then set it to 5:4 and now you're running the RAM at DDR400.