Human beings use the decimal system for numbers. We count from 0 to 9 before adding another digit in presenting the number. Computers, on the other hand, operate on bits (binary digits) and bytes. A number is represented internally in the computer by setting various bits on or off. For example, the number zero is represented by setting off all bits used for that number; and one, the lowest bit, on. Because a bit has only two states (on and off), to go to the next number (2), the lowest bit is turned off, while the next lowest bit is turned on. Such a system is recognized as the binary number system. This coding system can be depicted as follows:
Binary system 
Decimal system

0000  0 
0001  1 
0010  2 
0011  3 
0100  4 
0101  5 
0110  6 
0111  7 