A computer is a machine designed to perform work mathematically and to store and select in-formation that has been fed into it. It is run by either mechanical or electronic means. These ma-chines can do a great deal of complicated work in a very short time. A large computer, for exam-ple, can add or subtract nine thousand times a second, multiply a thousand times a second, or di-vide five hundred times a second. Its percentage of error is about one in a billion digits. It has been estimated that human beings making calculations average about one mistake per two hundred digits.
The heart of an electronic computer lies in its vacuum tubes, or transistors. Its electronic circuits work a thousand times faster than the nerve ceils in the human brain. A problem that might take a human being two years to solve can be solved by a computer in one minute, but in order to work properly, a computer must be given instructions—it must be programmed.
Computers can be designed for many specialized purposes, they can be used to prepare pay-rolls, guide airplane flights, direct traffic, even to play chess. Computers play an essential role in modern automation in many plants and factories throughout the world. The author calls the vacuum tubes the electronic computer"s ______.