Defrag doesn't operate on files per se, it runs defragmentation of a disk,
optimizing file storage by moving the little bits and pieces of files to
contiguous spaces on the disk.. Database files, such as Access, Outlook,
etc., need to be compacted/compressed to remove whitespace.
You can compact your PST file by right-clicking on the top-level folder,
going to properties, advanced, compact now... this will only make a
difference if you've deleted a lot of items and emptied the deleted items
folder, but is a good idea to run periodically. Also keep an eye on your PST
file size; it has a 2GB limit but you'll probably see problems crop up
closer to 1.2 - 1.5 GB.
