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big-endian

The adjectives big-endian and little-endian refer to which bytes are most significant in multi-byte data types and describe the order in which a sequence of bytes is stored in a computer's memory.

In a big-endian system, the most significant value in the sequence is stored at the lowest storage address (i.e., first). In a little-endian system, the least significant value in the sequence is stored first. For example, consider the number 1025 (2 to the tenth power plus one) stored in a 4-byte integer:

00000000 00000000 00000100 00000001

Address Big-Endian representation of 1025 Little-Endian representation of 1025
00
01
02
03
00000000
00000000
00000100
00000001
00000001
00000100
00000000
00000000

Many mainframe computers, particularly IBM mainframes, use a big-endian architecture. Most modern computers, including PCs, use the little-endian system. The PowerPC system is bi-endianbecause it can understand both systems.

Converting Data Between the Systems

Converting data between the two systems is sometimes referred to as the NUXI problem. Imagine the word UNIX stored in two 2-byte words. In a Big-Endian systems, it would be stored as UNIX. In a little-endian system, it would be stored as NUXI.

Note that the example above shows only big- and little-endian byte orders. The bit ordering within each byte can also be big- or little-endian, and some architectures actually use big-endian ordering for bits and little-endian ordering for bytes, or vice versa.

The terms big-endian and little-endian are derived from the Lilliputians of Gulliver's Travels, whose major political issue was whether soft-boiled eggs should be opened on the big side or the little side. Likewise, the big-/little-endian computer debate has much more to do with political issues than technological merits.







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