mostsignificantbit

Most significant bit, or MSB, refers to the bit in a binary number that has the greatest weight within a fixed-length word. In standard unsigned notation, the MSB is the leftmost bit. For an n-bit number, the MSB has weight 2^(n-1), while the remaining bits have weights 2^(n-2) down to 2^0. The MSB helps determine the overall magnitude and the range of values that can be represented.

In signed number representations, the MSB often serves as the sign bit. In two's complement, the MSB indicates whether the value is nonnegative or negative, but the remaining bits encode the magnitude in a way that allows simple arithmetic. Other schemes, such as sign-magnitude, also use the MSB as a sign indicator while encoding magnitude in the remaining bits.

The MSB is commonly used in bitwise operations and data processing. It can be extracted by shifting and masking, for example by shifting right by n-1 positions and taking the least significant bit. Determining whether a value lies in the upper or lower half of its range is a frequent MSB-based check. In certain encoding schemes, the MSB of a byte acts as a continuation flag, indicating whether more bytes follow.

Endianness relates to the order of bytes in multi-byte values rather than the bit significance within a single byte. In big-endian systems, the most significant byte is stored or transmitted first; within a byte, the MSB remains the highest-order bit. Understanding the MSB is fundamental to binary arithmetic, data representation, and various protocols.