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The partition boot sector is used to define all parameters on a FAT disk.  It will include cluster size, FAT lengths, and directory location, along with the directory length.

The media BIOS sector is normally the first sector on the partition. When this sector is missing, the details it normally contains must be filled in.  A very good start is to use the Analyse Disk Paramters function.  This function will scan the disk and calculate certain values based on the following.

Cluster Size

By finding two subdirectories, it is possible to work out the cluster size in sectors

FAT Start

A FAT normally starts with the hex codes F8 FF.  A FAT is also always near the start of a disk, so only the first 1000 sectors are searched for a FAT

FAT Length

If botn FATs can be found (in the fist 2000 sectors of the disk) then the FAT length can be calculated

DIR Start

For a FAT12 or FAT16 disk, the directory starts just after the second FAT. For FAT32, the root directory can be placed anywhere.

Cluster 2 Location

Cluster 2 is the location that data storage starts.  For a FAT12 and FAT16 disk, this is the location after the directory. For a FAT32 disk, is is normally the location after the second FAT map and may also be the start of the root directory.  Fortunately, it is possible to calculate this location from finding the location of any two subdirectories.

With much of data recovery, the automatic analysis may produce the correct results, but at times, they may need to be tinkered with .