What Is Directory Damage?
The directory is the portion of your disk set aside to record the names and locations of your files and folders. When your directory is either incorrectly updated or not updated at all, your directory is damaged.
If your Mac crashes or loses power, updated directory information that the OS X caches in memory for faster access never gets written to your disk, resulting in directory damage. The presence of directory damage may be very minor and go unnoticed. Or it could make some or all of your files inaccessible!
The continued accuracy of information in the directory depends on the ability of OS X to perform ALL of its update and maintenance operations without any unexpected interruptions. Also, to help speed up many computer operations, important pieces of information are temporarily cached in memory instead of being immediately saved to the disk.
Common types of unexpected interruptions are kernel panics and crashes, power loss (lights flicker), turning your OS X computer off without using the proper "Shut Down" procedure. Depending upon the exact moment of the interruption, you stand a good chance that your directory was either not updated correctly and/or some information had not been saved to the disk. You now have directory damage and/or information loss.
Another way that your directory can be damaged is if an errant program inadvertently writes its own data to the portion of the disk that is reserved for the directory. If this occurs, then your directory data has been overwritten and may be permanently lost. Also, system extensions, called kernel extensions in OS X, may inadvertently corrupt system data. Directory damage occurs when the directory containing the corrupt data is saved to disk.