Transistor is a tiny device that controls the flow of electric current in radios, television sets, computers, and almost every other kind of electronic equipment. Transistors vary in size from about a thousandth of a millimeter to a few centimeters across.

Transistors replaced electronic components called vacuum tubes almost completely in the 1950's and 1960's because they have a number of advantages over vacuum tubes. For example, transistors are smaller, lighter, less expensive to produce, cheaper to operate, and more reliable than vacuum tubes.

Transistors are the main components built into computer chips, devices that carry out computer programs and store programs and other data. Some chips no larger than a fingernail contain millions of transistors.

Large, individual transistors are called discrete transistors. Because of their size, these units can handle many times the power of transistors in chips. Uses of discrete transistors include providing the power for the speakers of high-fidelity sound systems, the transmitters of citizens band radios, and the motors of small appliances; turning lights on and off; and controlling energy flow through electric power lines.

Excerpt from the "Transistor" article, The World Book Encyclopedia © 1999