When you delete a file from your hard disk, it may seem as if it is gone forever. In truth, however, this is not the case. The seemingly permanent process of file deletion actually leaves the file data still on the hard disk. When a file is deleted, it is simply marked ‘deleted’, and the space that it occupies on the disk is accordingly marked ‘ready for use’. Hence, it may be overwritten when more disk space is required, but this is by no means certain, unless the entire hard disk is filled with data.
Now, the actual data that make up the file is still on the hard disk, even after deletion. This makes it available for recovery, usually done using specially designed data recovery programs. MSDOS, in fact, has a built-in UNDELETE command which may recover recently deleted files.
The reason why file deletion is not as thorough as it can be is a simple one; resource management. Actually overwriting every bit of every file that is to be deleted will use more resources than would be practical, for everyday use. And in fact, this simple file deletion is usually sufficient for the basic user’s needs.
However, security considerations might necessitate the complete erasure of a given hard disk or collection of hard disks. When reassigning hard disks, for instance, or switching computers around, confidential data might need to be deleted. To lessen the possibility that this data is recovered, a hard disk wipe may be performed.
When a hard disk wipe is performed, the entire area of the hard disk is actually overwritten with random data. This means that the data that used to be on the hard disk becomes much harder (practically impossible) to recover after such a process. Almost no traces of the previous data that used to be on the disk is left, making a hard disk wipe a secure improvement upon ordinary file deletion.
The metadata or information on the data that used to be on the hard disk is also wiped clean, since the entire space of the hard disk is overwritten. The randomness of this data used to overwrite depends on the algorithm used to generate it. Some hard disk wipe programs give users the choice to select the algorithm they want the program to use. However this is not as necessary for hard disk wipe programs as it is for file shredder programs, which wipe individual files. This is because when it is the entire hard disk that is wiped, the degree of randomness of the overwriting data is not anymore as important.
Performing a hard disk wipe is often as easy as clicking a few buttons in a specially designed hard disk wipe program. Some programs are set to run automatically when a CD containing the program is placed into the computer containing the hard disk to be wiped. This makes it easier to perform batch wipes on many computers at once, and makes the hard disk wipe a feasible security solution for multiple hard disks.