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Most significant bit

Most significant bit

(also MSB)

Most significant bit definition

The most significant bit (MSB) is the bit in a multiple-bit binary number representing the highest power of two in the number. Binary numbers are used in computing and other fields.

The MSB is usually the bit farthest to the left or the first transmitted bit in a sequence. For example, in the binary number 1000, the MSB is 1, while in the binary number 0111, the MSB is 0. The opposite of the MSB is the LSB — or the least significant bit. The LSB is usually the farthest number to the right (or last).

See also: 128-bit encryption, data transmission

How does the most significant bit (MSB) work?

  • A binary number is a number represented using only two digits, 0 and 1.
  • Each digit in the binary number represents a power of 2 (with the farthest digit on the right representing 2^0, the next digit representing 2^1, and so on).
  • The most significant bit (MSB) is the leftmost number representing the highest power of 2 in the binary number. The value of MSB is equal to 2^(n-1), where n is the total number of bits in the binary number.

Where MSBs are used

Binary numbers are used in computing and several other areas.

  • Digital signal processing. In digital signal processing, the MSB represents the sign of a number. For example, the MSB may be used to indicate if a number is positive or negative: a value of 0 indicates a positive number, while a value of 1 indicates a negative number.
  • Image processing. In image processing, the MSB represents the brightness of a pixel. For example, in grayscale images, the MSB represents the brightest shade of gray, with other bits representing progressively darker shades.
  • Data transmission. In data transmission, the MSB is used to indicate the start of a message (or packet of data). In asynchronous serial communication, the transmission of a start bit with a 0 value signals the beginning of a data byte.
  • Error correction. In error correction algorithms, the MSB detects errors in transmitted data. If the MSB doesn’t match the expected value, an error is detected.

Further reading

Ultimate digital security