Defragmenting your Mac's hard disk

This document discusses hard disk fragmentation, and what you can do about it.

Note: This document applies to Mac OS 9 and earlier. For information about Mac OS X, see technical document 25668.

This article has been archived and is no longer updated by Apple.

Fragmentation occurs when files are deleted and created. For example, suppose you create three files, then delete the second one. If you save a fourth file, which is larger than the size of the second file, the Macintosh file system may put a portion of the fourth file in the space occupied by the second file, and put the remainder after the third file. To access the entire file, the system has to look in two places.

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. You should not need to frequently defragment the computer's hard disk.

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 disk 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 third-party defragmenting software (see below), or back up your hard disk and use Apple Drive Setup to initialize the disk, then restore your files.

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

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.

You should keep a current backup of your hard disk, especially before using defragmentation software.

What third-party software can I use?

Apple does not endorse any single defragmenting utility, but you may wish to search for available third-party solutions in the Macintosh Products Guide (

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