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Binary representation

A positional number system represents a number using digits whose values depend on position. Ordinary decimal notation uses powers of ten; binary uses only the digits $0$ and $1$ and powers of two.

For example,

$$1011_2=1\cdot2^3+0\cdot2^2+1\cdot2^1+1\cdot2^0=11_{10}.$$

Place values

Moving one binary position to the left multiplies the place value by two:

... 16  8  4  2  1
     1  0  1  1

The pattern 1011 therefore selects $8+2+1$.

Converting to binary

A nonnegative integer can be written as a sum of powers of two. For example,

$$13=8+4+1,$$

so

$$13_{10}=1101_2.$$

Why binary is useful

Physical digital systems can reliably distinguish two states, so binary symbols map naturally to electronic representations.

Binary notation is still just a representation of a number. The same numerical value can be written in decimal, binary, hexadecimal or another base without changing the underlying quantity.