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Endianness

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Endianness is a fundamental concept in computer science regarding data organization. It describes the specific order in which bytes are transmitted or stored in memory. When a computer handles a large group of data, called a word, it must decide how to arrange the individual bytes. This arrangement is based on byte significance, which refers to the mathematical weight of each byte within the larger value.

32bit-Endianess
32bit-Endianess

To understand the mechanism, one must look at how computer memory is structured. Memory consists of a sequence of storage cells called bytes, which are eight bits long. Each byte is assigned a unique memory address used for access. When a data field contains multiple bytes, the computer must order them. In a big-endian system, the most significant byte is stored at the smallest memory address. This is the byte that carries the highest numerical value. Conversely, a little-endian system stores the least significant byte at the smallest address.

32bit-Endianess
32bit-Endianess

There are several distinct types of endianness used in digital engineering. The two primary types are big-endian (BE) and little-endian (LE). Big-endian is similar to how humans write numbers in English, placing the most important digits on the left. Little-endian reverses this logic in memory. Some specialized architectures are described as bi-endian. These machines have the ability to switch their endianness during data fetches or stores. Other, more complex arrangements are called middle-endian or mixed-endian.

32bit-Endianess
32bit-Endianess

The terms used to describe these systems have a literary origin. In 1980, Danny Cohen introduced the terms in an Internet Experiment Note. He borrowed the names from Jonathan Swift’s 1726 satirical novel, Gulliver’s Travels.

Gullivers travels
Gullivers travels

In the book, residents of the land of Lilliput engage in a fierce debate. They argue over whether a boiled egg should be broken at the big end or the little end. The scholars who prefer the big end are called Big-Endians, while those who prefer the little end are Little-Endians.

Different technologies rely on different endianness for specific tasks. Big-endian is the dominant standard for networking protocols. In the Internet protocol suite, this is specifically referred to as network order. This ensures that the most significant byte is transmitted first across the network. On the other hand, little-endian is the dominant ordering for many processor architectures. This includes the x86 family used in many computers and most ARM implementations.

32bit-Endianess
32bit-Endianess

Endianness can cause interesting challenges when data moves between different systems. If a little-endian machine reads a text string like "JOHN" stored as an integer, it might appear as "NH OJ". This happens because the bytes are interpreted in a different sequence. To fix this, engineers use a process called byte-swapping. Byte-swapping rearranges the bytes to convert one endianness to another. Many modern compilers and CPU instruction sets, such as those in x86 or ARMv6, provide native support for this task.

32bit-Endianess
32bit-Endianess

Understanding these orders is important for hardware efficiency and mathematical operations. For example, addition, subtraction, and multiplication often start at the least significant digit. Because of this, little-endian machines can find the implementation of these operations marginally simpler. However, comparison and division operations typically start at the most significant digit. This makes big-endian machines slightly more efficient for those specific tasks.

32bit-Endianess
32bit-Endianess
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