When the user requests to delete a file, most modern operating systems do not erase the actual data. Instead, they merely erase a pointer to the file so that the file does not appear in directory listings. These files can be recovered by simply undeleting the file — that is, restoring the directory entry.
For some file systems, such as FAT, the deleted directory entry itself is easily recovered. In these cases the files can be recovered using an undelete program. In other cases, however, the directory entry is not available — perhaps because it was overwritten. In these cases the only way that the file can be recovered is through the use of File Carving.
Using an undelete function on FAT32 can be very dangerous if any files are fragmented. Deleting the file also removes the FAT entry and so the locations of split fragments can no longer be assumed. Forensically, making any changes to a disk is 'not allowed'.