The **binary system** uses the number 2 as its base. This means, the only digits used in this system are 0 and 1. The binary system can be applied easily to PLCs.

For example, to distinguish between two voltage levels (5V and 0V), the two levels can be related to the binary digits 1 and 0 where the high voltage is 1 and the low voltage is 0.

Each position in a binary number can only use two digits; therefore each position of a binary number can go through only two changes.

Rather than the weighted value being 10 raised to the power of the position (as with the decimal system), for the binary system, the weighted value is 2 raised to the power of the position.

In the binary system, each digit is called a “bit” (refer to Module 5, Memory Organization for more information about bits). Bits combine to form “words” which refer to a location in the PLC processor-memory element.

The binary system only uses two digits, but it can be used to represent any quantity that the decimal system can represent. All computer memory uses the binary system to preform internal functions and to store data.