Unit content
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.