This article discusses disk drive fragmentation and what to do about it.

The file system used on Macintosh computers is designed to work with a certain degree of fragmentation. This is normal and does not significantly affect performance for the majority of users and you should not need to defragment your hard disk frequently.

In reality, however, the nature of the files, the nature of the work you are doing, the nature of random-access disk mechanisms and the exact order in which the files are segmented can all have a bearing on the resulting performance. In general, there is not significant degradation of performance from normal use of your computer.

If you create and delete a large number of files, your hard drive may become fragmented to the point that you may see a slight slow-down of file system performance. At this point you can either use a defragmenting utility, or back up your hard disk, use Apple Drive Setup to reinitialize it, then restore your files.

WARNING: Reinitializing erases all the files on your hard drive. Make sure you have a complete backup because you will need to restore all your files once initialization is complete.

Note: The defragmenting process generally results in a large amount of disk activity due to the amount of data being rearranged. Some disk defragmenting software packages also cannot completely recover if a critical portion of data on the hard disk should be in "transit" if the software fails. In this instance you may run the risk of losing that specific file or all data on your hard drive.

Apple recommends keeping a current backup of your hard drive. You should fully backup your hard drive before running any defragmentation software.