There are two widespread types of data recovery - unformat and undelete.
"Undelete" usually describes a recovery of one file, or a few files from an properly functioning filesystem. What to expect from the undelete process in various filesystems is explained in detail at www.un-delete.com.
The term "unformat" usually means a recovery of multiple files off the damaged volume on which none of the files are accessible any longer.
The "undelete" software assumes that the filesystem is OK, all but one sought-for file. Conversely, for the "unformat", the data recovery software must expect to properly work around some massive glitches of the partition, for even the quick format overwrites parts of the filesystem with blank data.
If the files are recovered corrupt after unformat, it is in most cases pointless to apply a file data recovery software. The "undelete" is in most cases very quick and produces cleaner recovered files.
