Sector– A 512-byte packet of data in EIDE and SCSI hard drives. The smallest amount of data can be written or read to the drive from the host interface. On UNIX and Macintosh drives, sectors are grouped into blocks or logical blocks that are often defined as a single sector. The terms block and sector are sometimes used interchangeably according to the context. (Note: The meaning of the term block in connection with the physical configuration of the disk is different from its meaning at the system level. (See also block and cluster.)