Unallocated Space

computer operating systems, such as Windows, allocate space on the hard drive as adjacent groups of sectors, known as allocation units, or clusters. When you create a new file, the operating system finds available space and allocates that space to the file. Unallocated space is space that is not allocated to active files within a file system.

The type of object that you can create in unallocated space depends on whether your hard disk is a basic disk, containing primary partitions, extended partitions and logical drives, or a dynamic disk, containing volumes that span multiple disks. In the case of a basic hard disk, you can use unallocated space outside an existing partition, or logical storage unit, to create a primary partition -- typically, the partition used to start the operating system -- or an extended partition. Similarly, you can use unallocated space inside an existing partition to create logical drives, or parts of the same physical disk that are managed as independent units.