The area of computer media, such as a hard drive, that does not contain normally accessible data. Unallocated space is usually the result of a file being deleted. When a file is deleted, it is not actually erased, but is simply no longer accessible through normal means. The space that it occupied becomes unallocated space, i.e., space on the drive that can be reused to store new information. Until portions of the unallocated space are used for new data storage, in most instances, the old data remains and can be retrieved using forensic techniques.
Available disk space that is not allocated to any volume. The type of volume that you can create on unallocated space depends on the disk type. On basic disks, you can use unallocated space to create primary or extended partitions. On dynamic disks, you can use unallocated space to create dynamic volumes. See also: basic disk; dynamic disk; extended partition; logical drive; object; partition; primary partition; volume