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In , the least significant bit ( LSB) is the position in a binary giving the units value, that is, determining whether the number is even or odd. The LSB is sometimes referred to as the right-most bit, due to the convention in positional notation of writing less significant digits further to the right. It is analogous to the least significant of a integer, which is the digit in the ones (right-most) position.

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<sup>31</sup>..2<sup>0</sup>). Although a few CPU manufacturers assign the opposite way (which is not the same as different ), the term least significant bit itself remains unambiguous as an alias for the unit bit.

By extension, the least significant bits (plural) are the bits of the number closest to, and including, the LSB.

The least significant bits have the useful property of changing rapidly if the number changes even slightly. For example, if 1 (binary 00000001) is added to 3 (binary 00000011), the result will be 4 (binary 00000100) and three of the least significant bits will change (011 to 100). By contrast, the three most significant bits (MSBs) stay unchanged (000 to 000).

Least significant bits are frequently employed in pseudorandom number generators, tools, and .


Unsigned integer example
This table illustrates an example of decimal value of 149 and the location of LSB. In this particular example, the position of unit value (decimal 1 or 0) is located in bit position 0 ( n=0). MSB stands for Most Significant Bit, while LSB stands for Least Significant Bit.
Binary (Decimal: 149)10010101
Bit weight for given bit position n ( 2n )2726252423222120
Bit position labelMSB__________________LSB
Position of LSB is independent of how the bit position is transmitted (Some system transmit MSB first, others transmit LSB first), which is a question more of a topic of .


Least significant bit in digital steganography

In digital , sensitive messages may be concealed by manipulating and storing information in the least significant bits of an image or a sound file. In the context of an image, if a user were to manipulate the last two bits of a color in a pixel, the value of the color would change at most +/- 3 value places, which is likely to be indistinguishable by the human eye. The user may later recover this information by extracting the least significant bits of the manipulated pixels to recover the original message.

This allows for the storage or transfer of digital information to be kept concealed.


Least significant byte
LSB can also stand for least significant byte. The meaning is parallel to the above: it is the (or octet) in that position of a multi-byte number which has the least potential value. If the abbreviation's meaning least significant byte isn't obvious from context, it should be stated explicitly to avoid confusion with least significant bit.

To avoid this ambiguity, the less abbreviated terms "lsbit" or "lsbyte" are often used.


See also

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