Short for logical unit number, a unique identifier used on a SCSI bus to distinguish between devices that share the same bus. SCSI is a parallel interface that allows up to 16 devices to be connected along a single cable. The cable and the host adapter form the SCSI bus, and this operates independently of the rest of the computer. Each of the eight devices is given a unique address by the SCSI BIOS, ranging from 0 to 7 for an 8-bit bus or 0 to 15 for a 16-bit bus. Devices that request I/O processes are called initiators. Targets are devices that perform operations requested by initiators. Each target can accommodate up to eight other devices, known as logical units, and each is assigned an LUN. Commands that are sent to the SCSI controller identify devices based on their LUNs.