Big and Little Endians

Byte Order in Multibyte Values

HP, IBM and Motorola 68000 systems store multibyte values in Big Endian order, while Intel 80x86 and DEC VAX systems store them in Little Endian order. Big Endian stores the high-order byte at the starting address while Little Endian stores the low-order byte at the starting address. The low-order byte contains the bits for the lowest possible values, that is, 0-255, while the high-order byte contains the bits that specify the large values (that is, 256-65535 in a short integer). (The term endian is derived from a passage in Jonathan Swift's Gulliver's Travels). Swapping integer data between computers of different types is a difficult problem unless you convert the information into ASCII characters.

Sockets has functions to convert Long and Short Integers to and from Internet standard byte ordering, which is Big Endian.

htonl, convert host-to-network, long integer
htons, convert host-to-network, short integer
ntohl, convert network-to-host, long integer
ntohs, convert network-to-host, short integer

Big Endian systems such as HP-UX and MPE are already compatible with the network ordering, so they can define these functions as null macros.

The Power PC is a bi-endian processor; that is, it supports both big- and little-endian addressing modes. This bi-endian architecture enables software developers to choose either mode when migrating OSes and applications from other machines.