Cluster – Windows allocate space to files in units called Clusters. Each cluster contains from 1 to 64 sectors, depending on the type and size of the Disk. A cluster is the smallest unit of Disk space that can be allocated for the usage by the files. A hard disk term refers to a group of sectors, the smallest storage unit recognized by the DOS. On the most modern hard disk, 512-byte sectors make up a cluster, and one or more clusters make up a track.