An organizationally unique identifier (OUI) is a 24-bit number that uniquely identifies a vendor, manufacturer, or other organization. These are purchased from the Institute of Electrical and Electronics Engineers, Incorporated (IEEE) Registration Authority by the "assignee" (IEEE term for the vendor, manufacturer, or other organization). They are used as the first portion of derivative identifiers to uniquely identify a particular piece of equipment as Ethernet MAC addresses, Subnetwork Access Protocol protocol identifiers, World Wide Names for Fibre Channel host bus adapters, and other Fibre Channel and Serial Attached SCSI devices.