address

Label assigned to the components of a computer system for the purpose of directing data to a specific location. A memory address is used to locate data in memory, a Medium Access Control (MAC) address and network address locate a computer that is attached to a network, and an e-mail address is used to ensure e-mail messages are delivered to the correct recipient.

Memory address Unique address by which a word, or byte, of computer memory can be located. Different computer architectures may use different addressing methods. The number of bits that are used for the memory address will determine the maximum amount of memory that a computer can have. This is normally measured in units of 1,024 bytes (known as kilobytes, or K). Hence a computer with 32 bit addressing can have more memory than a computer which only uses 16 bits for addressing. The set of all memory addresses available to a computer program is called an address space.

MAC address The MAC address is used at the lowest level when computers are joined together on a network. The address is set on the network interface card (NIC) when it is manufactured. MAC refers to the procedure used by the network architecture to ensure that transmissions occur in an orderly way.

Network address When computers are connected together on a network each one has a unique address. Different types of network may use different styles of address. Every computer on the Internet, for example, has a unique address consisting of four numbers, joined together by dots, for example ‘127.0.0.1’ – this is sometimes called the dotted-decimal or IP (Internet Protocol) address. In addition, each computer on the Internet may have a more human-friendly name of the form ‘anymc.anyco.com’. This refers to a computer called ‘anymc’ in the domain ‘anyco’, in the top-level domain ‘com’. Anytime a computer's name is specified in this way the name has to be translated into the dotted-decimal form. The translation records are managed by the domain name server (DNS).

Internet e-mail address These are made up of two parts, a user name and a host part, separated by an @ symbol. Sending an e-mail to ‘bob@anyco.com’, for example, would identify a user called ‘bob’ at e-mail server ‘anyco.com’. The combination of user name and host part of an address must be unique. Other types of e-mail system may have different addressing schemes.