Preaching to the converted it may be, but drive fragmentation is a pain. As you run your PC, loading and saving files, the filing system saves them in any convenient spaces it can find on your hard drive. It'll happily break up a file into small pieces in order to fit it into available gaps in the file structure.

When asked to load a fragmented file, it takes longer for the filing system to collect the pieces together, than to load it in one chunk. Filing performance can be increased by putting the file fragments back together by 'defragmenting'.

Windows XP comes with a disk defragmentation routine, but Diskeeper would like you to forsake that for its own eponymous utility. Now in version 2007 - effectively version 11 - this is a mature product, which benefits from more than 10 years of development.

The big advance in the 2007 version is what Diskeeper calls InvisiTasking. This means the program will sit in the background, using system resources when you're not working on your PC. You no longer need to schedule drive defragmentation at regular intervals; files are automatically defragmented whenever they're broken up.

This makes Diskeeper 2007 a load-and forget application, which needs little configuration. In fact, it's best to run it in automatic mode, since running a manual defragmentation can take a long time. Our test machine took more than 24 hours for the first run.

Fragmentation is reduced and Diskeeper aims for the best performance from your files, not the prettiest file structure diagram. If a file is loading fast, it doesn't get moved around. The program uses another technology, I-FAAST 2, to monitor which files are used most often and places them in the fastest area of the hard drive. Under test, using Diskeeper's own load monitor, InvisiTasking used between one and eight per cent of system resources while running, and pulled back as soon as any other task started. You shouldn't notice any performance hit.

Diskeeper does the job it claims to do and its new real-time, behind-the scenes techniques mean it works well straight from the box. A price of £90 is a lot for defragmenting your hard drive, but this is the premium edition and versions for home and basic office use start at £23.