# Most significant bit

In computing, the **most significant bit** (**MSB**, also called the **high-order bit**) is the bit position in a binary number having the greatest value. The MSB is sometimes referred to as the **left-most bit** due to the convention in positional notation of writing more significant digits further to the left.

The MSB can also correspond to the sign bit of a signed binary number in one's or two's complement notation, "1" meaning negative and "0" meaning positive.

It is common to assign each bit a position number, ranging from zero to N-1, where N is the number of bits in the binary representation used. Normally, this is simply the exponent for the corresponding bit weight in base-2 (such as in `2`

). Although a few CPU manufacturers assign bit numbers the opposite way (which is not the same as different endianness), the ^{31}..2^{0}*MSB* unambiguously remains the *most* significant bit. This may be one of the reasons why the term *MSB* is often used instead of a bit number, although the primary reason is probably that different number representations use different numbers of bits.

By extension, the **most significant bits** (plural) are the bits closest to, and including, the MSB.

## Most Significant Bit First vs Least Significant Bit First

The expressions *Most Significant Bit First* and *Least Significant Bit First* are indications on the ordering of the sequence of the bits in the bytes sent over a wire in a transmission protocol or in a stream (e.g. an audio stream).

*Most Significant Bit First* means that the most significant bit will arrive first: hence e.g. the hexadecimal number `0x12`

, `00010010`

in binary representation, will arrive as the sequence `0 0 0 1 0 0 1 0`

.

*Least Significant Bit First* means that the least significant bit will arrive first: hence e.g. the same hexadecimal number `0x12`

, again `00010010`

in binary representation, will arrive as the (reversed) sequence `0 1 0 0 1 0 0 0`

.

## Other uses

**MSB** can also stand for "**most significant byte**".

^{[1]}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.

To avoid this ambiguity, the less abbreviated terms "**msbit**" or "**msbyte**" are often used.

## See also

## References

- ↑ Rouse, Margaret (September 2005). "most significant bit or byte". TechTarget.