|  | 6.2 | Hexadecimal Numbers
| 6.2.1 | Hexadecimal numbers as MAC addresses

You have already studied the decimal and binary numbering systems. Decimal numbers express a Base 10 system, and binary numbers express a Base 2 system. Another numbering system you need to learn is the hexadecimal (hex) or base 16 system. You will learn about the hex numbering system on the following pages. Hex is a shorthand method for representing the 8-bit bytes that are stored in the computer system. It was chosen to represent identifiers because it can easily represent the 8-bit byte by using only two hexadecimal symbols.

MAC addresses are 48 bits in length and are expressed as twelve hexadecimal digits. The first six hexadecimal digits, which are administered by the IEEE, identify the manufacturer or vendor and thus comprise the Organizational Unique Identifier (OUI). The remaining six hexadecimal digits comprise the interface serial number, or another value administered by the specific vendor. MAC addresses are sometimes referred to as burned-in addresses (BIAs) because they are burned into read-only memory (ROM) and are copied into random-access memory (RAM) when the NIC initializes.

To learn more about how these OUIs are assigned, and to search for current address assignments, go to:

| Web Links
| OUIs Frequently Asked Questions
| Hex (hexadecimal) Explained