File systems have been used for organizing data in computers since data began to be stored in them. As an early entrant, the FAT file system has attained a certain ubiquity and almost all operating systems offer it in some form. Why? Because its simplicity makes it easy to understand and implement and its ubiquity makes it a common denominator presumed to provide interoperability among systems. In this paper, we examine the underlying mechanisms used by the original DOS file system, some characteristics that leave it vulnerable to corruption, and some of the ways that vendors (including Microsoft) are trying to make it more reliable for today’s users.