资料题：The speed with which an electronic computer works depends an its（　）。

A computer is a machine designed to perform work mathematically and to store and select information that has been fed into it.It is run by either mechanical or electronic means.These machines can do a great deal complicated work in a very short time.A large computer, for example, can add or subtract nine thousand times a second, multiply a thousand times a second, or divide five hundred times a second.It's percentage of error is about one in a billion 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 time faster than the nerve ells 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 mist be given instructions- it must be programmed.Computers can be designed for many specialized purposes.They can be used to prepare payrolls, guide airplane lights, direct traffic, even to play chess.Computers play an essential role in modem automation in many plants and factories throughout the world.