Defining Endianness
Endianness refers to the order or sequence of bytes of a multi-byte data type (like integers, floating-point numbers, or addresses) when stored in computer memory. Since memory is byte-addressable, a multi-byte value occupies several consecutive memory locations, and endianness dictates which byte (most significant or least significant) is stored at the lowest memory address.
Big-Endian vs. Little-Endian
There are two primary types: Big-Endian and Little-Endian. In a Big-Endian system, the most significant byte (MSB) of a multi-byte value is stored at the smallest memory address, with subsequent bytes stored in increasing memory addresses. Conversely, in a Little-Endian system, the least significant byte (LSB) is stored at the smallest memory address, followed by the more significant bytes in ascending order.
Illustrative Example
Consider the 4-byte hexadecimal number 0x12345678. In a Big-Endian system, this would be stored as: `0x12` at address `0x1000`, `0x34` at `0x1001`, `0x56` at `0x1002`, and `0x78` at `0x1003`. In contrast, a Little-Endian system would store it as: `0x78` at address `0x1000`, `0x56` at `0x1001`, `0x34` at `0x1002`, and `0x12` at `0x1003`. The value itself is the same, but its representation in memory differs.
Importance and Applications
Endianness is crucial for ensuring data compatibility when transferring data between different computer architectures or systems, especially over networks. If a Big-Endian system sends data to a Little-Endian system without proper conversion, the receiving system will misinterpret the byte order, leading to incorrect values. Network protocols often define a specific byte order (network byte order, typically Big-Endian) to standardize data transmission and avoid such issues.