= Most significant bit
= MSB
{c}
{synonym}
The <most significant bit> is the <binary digit> with greatest positional weight in a specified binary representation. For a positive <integer> written without leading zeros, it is the leading one: in $13=(1101)_2$, it has weight $2^3$.
For a fixed-width word, the term instead denotes the leftmost position even when that bit is zero. In two's-complement signed representation, that position is the sign bit. Stating the width and whether the value is signed prevents confusing the highest position of a word with the highest nonzero bit of an <integer>.
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