They're probably referring to a process called 'overburning' in which areas on the outer edge of the disc is recorded onto, when they are usually not. This sometimes causes incompatibility, and doesn't gives such an enormous performance boost (not a disk that I have heard of). Since most discs are not exactly 650 or 700 megs , YMMV depending on what their actual capacity is. They are several apps that will allow you to overburn (or oversize) on a mac.