(Or "MAC address") The physical address identifying an individual Ethernet controller board. An Ethernet addess is a 48-bit number aabbccddeeff where a-f are hexadecimal digits. The first 24 bits, aabbcc, identify the manufacturer of the controller. The Ethernet address is hard-wired on some controllers, stored in a ROM on some, and others allow it to be changed from software. It is usually written as six hexadecimal numbers, e.g. 08:00:20:03:72:DC.