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Endianness refers to the order of the bytes, comprising a digital word, in computer memory. It also describes the order of byte transmission over a digital link. Words may be represented in big-endian or little-endian format. With big-endian the most-significant byte of a word is stored at a particular memory address and the subsequent bytes are stored in the following higher memory addresses, the least significant byte thus being stored at the highest memory address. Little-endian format reverses the order and stores the least-significant byte at the lower memory address with the most significant byte being stored at the highest memory address.〔(University of Maryland - Definitions ). Accessed 26 Sept 2014〕 Both forms of endianness are widely used in digital electronics. The choice of endianness for a new design is often arbitrary, but later technology revisions and updates perpetuate the existing endianness and many other design attributes to maintain backward compatibility. As examples, the IBM z/Architecture mainframes use big-endian while the Intel x86 processors use little-endian. The designers chose endianness in the 1960s and 1970s respectively. Big-endian is the most common format in data networking; fields in the protocols of the Internet protocol suite, such as IPv4, IPv6, TCP, and UDP, are transmitted in big-endian order. For this reason, big-endian byte order is also referred to as network byte order. Little-endian storage is popular for microprocessors, in part due to significant influence on microprocessor designs by Intel Corporation. Mixed forms also exist, for instance the ordering of bytes in a 16-bit word may differ from the ordering of 16-bit words within a 32-bit word. Such cases are sometimes referred to as mixed-endian or middle-endian. There are also some bi-endian processors that operate in either little-endian or big-endian mode. ==Illustration== Endianness may be demonstrated by writing a decimal number on paper in the conventional way which uses positional notation. The digits are written left to right, with the most significant digit to the left, which is analogous to the lowest address of memory used to store a number. For example, the number ''123'', has the hundreds-digit, ''1'', left-most which is understood by a numerate reader. This is an example of a big-endian convention taken from daily life. The little-endian way of writing the same number would place the digit ''1'' in the right-most position: ''321''. A person following conventional place-value order, who is not aware of this special ordering, would read the number as three hundred and twenty one. Endianness in computing is similar, but it applies to the ordering of bytes in memory or during transmission. The illustrations to the right, where ''a'' is a memory address, show big-endian and little-endian storage in memory. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「endianness」の詳細全文を読む スポンサード リンク
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