To compare numbers is the responsibility of the logical unit in the CPU of a computer.
A logical unit is a device or application program by which an end user (an application program, a terminal user, or an input/output mechanism) gains access to a SNA network.
In a SAN fabric, LUN storage is essential to the configuration of the environment and its performance. A LUN is a unique identifier given to separate devices, or logical units, so they can be accessed by a SCSI, iSCSI or Fibre Channel protocol.
In computer storage, a logical unit number, or LUN, is a number used to identify a logical unit, which is a device addressed by the SCSI protocol or Storage Area Network protocols which encapsulate SCSI, such as Fibre Channel or iSCSI.
A LUN may be used with any device which supports read/write operations, such as a tape drive, but is most often used to refer to a logical disk as created on a SAN. Though not technically correct, the term "LUN" is often also used to refer to the logical disk itself.