Most significant bit
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In computing, the most significant bit (msb) is the bit position in a binary number having the greatest value. The msb is sometimes referred to as the left-most bit on big-endian architectures, due to the convention in positional notation of writing more significant digits further to the left.
The msb can also correspond to the sign of a signed binary number in one or two's complement notation. "1" meaning negative and "0" meaning positive.
MSB, in all capitals, can also stand for "most significant byte". The meaning is parallel to the above: it is the byte (or octet) in that position of a multi-byte number which has the greatest potential value.
By extension, the most significant bits (plural) are the bits of the number closest to, and including, the msb.
[edit] Conventions
In referencing specific bits within a binary number, it is common to assign each bit a bit number, ranging from zero upwards to one less than the number of bits in the number. However, the order used for this assignment may be in either direction, and both orderings are used (in different contexts). This is one reason why "msb" is often used to designate the high-order bit instead of a bit number (which has greater potential for confusion).
