4.  Internal address representation

      Common to all portions of the system are two data structures. These structures are used to represent addresses and various data objects. Addresses, internally are described by the sockaddr structure,

struct sockaddr {
	short	sa_family;	/* data format identifier */
	char	sa_data[14];	/* address */
All addresses belong to one or more address families which define their format and interpretation. The sa_family field indicates the address family to which the address belongs, and the sa_data field contains the actual data value. The size of the data field, 14 bytes, was selected based on a study of current address formats.* Specific address formats use private structure definitions that define the format of the data field. The system interface supports larger address structures, although address-family-independent support facilities, for example routing and raw socket interfaces, provide only 14 bytes for address storage. Protocols that do not use those facilities (e.g, the current Unix domain) may use larger data areas.