FAT Format: Each cell in the FAT is one cluster of the disk. Each cell contains either a number, or an EOF (end of file) value. (Alternately, it can also contain a "bad sector" marking, indicating that that cluster contains a bad sector.) If this number is 0, that means that that cluster is "Available", i.e. it has no part of a file stored in it. Otherwise, the number is the next cluster at which the next piece of the file is. For example, suppose you have a file which occupies two clusters; The first is cluster 317, and the second is cluster 582. Cluster 317's cell in the FAT would contain the number 582 (because that's where the next cluster of the file is), while cluster 582's cell would contain an EOF. (As a side note, a "bad" entry in an FAT is actually the hex number FFF7, while an "EOF" entry can actually be any hex number from FFF8 to FFFF.)