FAT Filesystems

published 14 Jan 2010.

Whilst tinkering with FAT filesystems on small memory devices I found a number of resources that explained the intricacies better than most.

General Resources

Background on wiki http://en.wikipedia.org/wiki/File_Allocation_Table

Visual Representations of the FAT Structures

A series of posts by iprinceps.

• File system #1 - the structure of FAT file system http://iprinceps.egloos.com/1331268
• File system #2 - the boot record http://iprinceps.egloos.com/1331477
• File system #3 - boot record items only for FAT16 http://iprinceps.egloos.com/1333168
• File system #4 - boot record items only for FAT32 http://iprinceps.egloos.com/1333226
• File system #5 - the end of the boot record http://iprinceps.egloos.com/1343511
• File system #6 - the File system information (FSInfo) http://iprinceps.egloos.com/1343583

Microsoft White Paper aka fatgen103

Microsoft Extensible Firmware Initiative

FAT32 File System Specification

FAT: General Overview of On-Disk Format

General google search http://www.google.com/search?q=fatgen103

PDF download http://staff.washington.edu/dittrich/misc/fatgen103.pdf

Perhaps the single most important paragraph in the document (page 14):

FAT Type Determination

There is considerable confusion over exactly how this works, which leads to many “off by 1”, “off by 2”, “off by 10”, and “massively off” errors. It is really quite simple how this works. The FAT type — one of FAT12, FAT16, or FAT32 — is determined by the count of clusters on the volume and nothing else.