The smallest granularity of disk storage addressing is called a disk block, or sometimes a disk sector. Groups of disk blocks are usually organized together into the smallest unit of storage that can be allocated, and this unit is called a disk cluster. The number of blocks in a cluster is the cluster factor, and is established when the disk volume is initialized. Each individual disk block is composed of five hundred twelve (512) bytes, or one-half kilobyte. Each byte is comprised of eight bits. A bit represents the smallest unit of information, typically refered to as a one or a zero. OpenVMS tends to uses base two notation for disk storage, while disk storage capacity specifications from most storage vendors will generally use base ten notation. An OpenVMS disk block is 512 bytes in size; this is one-half kilobyte in base two notation.