I'm defragmenting my hard drive (XP SP3) with PerfectDisk 7.0, and it finds 816,659 excess fragments when I ask for an analysis.

[update] Specifically, it shows that the 1TB disk is 14% fragmented with 19693 fragments and 816,659 excess fragments. About 20% of the disk is still free space.

What does excess fragments refer to? What is the difference between fragments and excess fragments?

I have had problems in the past where I defragmented a fragmented disk and many files were corrupted. It seemed as though "excess fragments" referred to orphan pieces, where the program couldn't find out where to put them.

If that was true, then defragmenting a disk resulted in many incomplete files, and in fact I defragmented a disk full of MP3's and got a lot of corrupted files as a result.

Instead, I started to simply format a separate disk and copy everything from one to the other. That way there were no orphan bits, and no file corruption.

Does anybody know what "excess fragments" really are?