FSB=Front Side Bus, which is clocked in MHz just like a processor is. Essentially, it is how fast the memory and processor communicate with each other. With that said, you're looking at a 266 MHz difference, which when it comes down to it isn't much. However, if you are a gamer, it matters. But for regular use, i.e. e-mail, word processing, internet, movies, etc... it doesn't matter much.