Endianness is the ordering or sequencing of bytes of a word of digital data in computer memory storage or during transmission. Words may be represented in big-endian or little-endian manner. Big-endian systems store the most-significant byte of a word at the smallest memory address and the least significant byte at the largest. A little-endian system, in contrast, stores the least-significant byte at the smallest address.Both forms of endianness are in widespread use in digital electronic engineering. The initial choice of endianness of 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 Intel x86 processor represents a common little-endian architecture, and IBM z/Architecture mainframes are big-endian processors. The designers of these two processor architectures decided on endianness in the 1960s and 1970s in their initial product introductions.Big-endian representation is the most common convention 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 historical influence on microprocessor designs by Intel Corporation. Mixed forms also exist, for instance the ordering of bytes within 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 which can operate either in little-endian or big-endian mode.