the memory and FSB are in a ratio, and when you have it set to auto it's usually an 1:1 ratio, as you turn the FSB up from say 200 to 205, the memory clock will also go from 200 to 205, or 410 effective DDR sped, but since you have a 2.53 it's like 133 right? so when you turn the FSB up to 140 you effectively overclock the memory to 280MHz