binary 
A numeric system that represents all numbers using only two digits: 1 and 0. This system is used by computers because each binary digit can be represented by a single digital switch set to either on or off. Each of these digital switches is called a bit. An 8-bit computer processor represents data using sets of 8 bits, a 16-bit processor uses 16 bits, and so on. The more bits a computer can process at once, the larger the numbers it can work with.