Slack Space

Slack space is the unused storage space on hard disks. It is the remaining storage capacity between the end of a stored data file and the end of the physical sector. Since stored data files do not occupy the entire sector, there is always an unused remainder. This is the slack space.

The file systems of the DOS operating system and Windows store their files on the hard disks( HD) divided into sectors. When files are stored, these sectors, which have a size of 512 bytes, are not completely filled, so there is a remaining unused space available. This storage capacity is called slack space. For example, if a text file of 450 bytes is stored in a sector, then 62 bytes of unused storage space, Slack Space, remain on a new hard disk. No data is stored in this Slack Space.

During the erase process, the space is only made available for overwriting. This means that when a new smaller file is written, the Slack Space still increases, by the difference between the previously stored file and the new file plus the existing Slack Space. If the new file is 300 bytes, then the difference from the previous 150 bytes plus the existing slack space of 62 bytes gives a total slack space of 212 bytes.