Chapter 2 -Computer Logic.

2-State Devices [Bistable Devices]
A two-state device can be in only one of 2 possible states at any given time. These may be either ON or OFF.

A computer isn't built from light switches or light bulbs but is built using a wide range of devices. Today, the elementary building block for all modern computer systems is the transistor. A transistor is much like the light switch. It can be in an OFF state in which does not let electricity to flow or in an ON state, in which electricity can pass freely.

BinaryComputer people, however, do not like talking about the presence or absence of electrical charges. They prefer to represent this using binary. Binary is a number system. It is the ideal number system to represent two-states because it has only two digits: 0 and 1. It is important the in the number system we use in everyday life, ten digits are used: 0,1,2,3,4,5,6,7,8,9.