Sector zero contains a small program which instructs the computer to read sectors 0 through 9 of track zero into memory using part of the ROM boot code (rereading sector 0 in the process). The program in sectors 1–9 of track 0, including the complete RWTS code, then proceeds to load tracks 1 and 2, which contain the rest of DOS. On a system master disk, code is also included to determine the computer's RAM configuration and relocate DOS as high into system memory as possible, up to the 48 KB limit of the Apple II's main memory ($BFFF16).