File allocation table (FAT)
From The Glossary of Digital Photography
The primary file system for Windows-based computers, disk drives, and digital memory cards for cameras. FAT is a table that tells the computer where the pieces of a file are stored on a hard drive. The description usually contains the number of bits that it supports, such as FAT12, FAT16, and FAT32. A simple system that was designed in 1977 by Microsoft, FAT is prone to fragmentation, where bits and pieces of a file are spread out over the entire disk. Drives that use this format must be periodically defragmented. The Macintosh operating system can read and use the FAT file format, except on the boot disk drive.
