My physical hard drive is partitioned into C: (15.5 GB FAT32) and D: (41.6 GB NTFS). My computer is a Sony VAIO that I bought in 2001, and it was partitioned this way when I bought it. When I run Erase Unused Space on drive D:, there is not much change in the amount of unused space, but when I run it on drive C:, the unused space changes typically from about 2.6 GB to about 3.1 GB. I'm not complaining , but I'm curious why the unused space changes by such a larger amount in FAT32 than in NTFS.