Difference between Big Endian and little Endian Byte order

Question

what is the difference between Big Endian byte order and little Endian Byte order.

These both are related to Unicode and UTF16

where we use this?

Answer 1

Big Endian (BE) / Little Endian (LE) are two ways to organize multi-byte words. For example, when using two bytes to represent a character in UTF-16, there are two ways to represent the character 0x1234:

BE:  12 34
LE:  34 12

In order to decide if a text uses UTF-16BE or UTF-16LE, the specification recommends to prepend a Byte Order Mark (BOM) to the string, representing the character U+FEFF. So, if the first two bytes of a UTF-16 encoded text file are FE, FF, the encoding is UTF-16BE. For FF, FE, it is UTF-16LE.

A visual example: The word "Example" in different encodings (UTF-16 with BOM):

ASCII:     45 78 61 6d 70 6c 65
UTF-16BE:  FE FF 00 45 00 78 00 61 00 6d 00 70 00 6c 00 65
UTF-16LE:  FF FE 45 00 78 00 61 00 6d 00 70 00 6c 00 65 00

For further information, please read the Wikipedia page of Endianness and/or UTF-16.

Answer 2

UTF-16 encodes Unicode into 16-bit values. Most modern filesystems operate on 8-bit bytes. So, to save a UTF-16 encoded file to disk, for example, you have to decide which part of the 16-bit value goes in the first byte, and which goes into the second byte.

Wikipedia has a more complete explanation.

Answer 3

Byte endianness (big or little) needs to be specified for Unicode/UTF-16 encoding because for character codes that use more than a single byte, there is a choice of whether to read/write the most significant byte first or last. Unicode/UTF-16, since they are variable-length encodings (i.e. each char can be represented by one or several bytes) require this to be specified. (Note however that UTF-8 "words" are always 8-bits/one byte in length [though characters can be multiple points], therefore there is no problem with endianness.) If the encoder of a stream of bytes representing Unicode text and the decoder aren't agreed on which convention is being used, the wrong character code can be interpreted. For this reason, either the convention of endianness is known beforehand or more commonly a byte order mark is usually specified at the beginning of any Unicode text file/stream to indicate whethere big or little endian order is being used.

Answer 4

Ferdinand's answer (and others) are correct, but incomplete.

Big Endian (BE) / Little Endian (LE) have nothing to do with UTF-16 or UTF-32. They existed way before Unicode, and affect how the bytes of numbers get stored in the computer's memory. They depend on the processor.

If you have a number with the value 0x12345678 then in memory it will be represented as 12 34 56 78 (BE) or 78 56 32 12 (LE).

UTF-16 and UTF-32 happen to be represented on 2 respectively 4 bytes, so the order of the bytes respects the ordering that any number follows on that platform.

Answer 5

little-endian: adj.

Describes a computer architecture in which, within a given 16- or 32-bit word, bytes at lower addresses have lower significance (the word is stored ‘little-end-first’). The PDP-11 and VAX families of computers and Intel microprocessors and a lot of communications and networking hardware are little-endian. The term is sometimes used to describe the ordering of units other than bytes; most often, bits within a byte.

big-endian: adj.

[common; From Swift's Gulliver's Travels via the famous paper On Holy Wars and a Plea for Peace by Danny Cohen, USC/ISI IEN 137, dated April 1, 1980]

Describes a computer architecture in which, within a given multi-byte numeric representation, the most significant byte has the lowest address (the word is stored ‘big-end-first’). Most processors, including the IBM 370 family, the PDP-10, the Motorola microprocessor families, and most of the various RISC designs are big-endian. Big-endian byte order is also sometimes called network order.

---from the Jargon File: http://catb.org/~esr/jargon/html/index.html