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 machines can do a great deal of complicated work in a very shout time. a large computer, for example, can add or subtract nine thousand times a second, or divide five hundred times a second. It’s percentage of error is about one in a billion digits(数字). 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 cells 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 word properly, a computer must be given instructions and it must be programmed. Computers can be designed for many specialized purpo
A. make fewer errors
B. do not have to be programmed
C. work more quickly
D. understand their instructions
Passage Five
The computer is a wonderful machine. It is the most important invention since the type of engine used in cars. Today it has the greatest effect on science, industry and business, but it is being used more in education and medicine. By the end of this century it will touch the lives of everyone, even people in distant villages. It is a revolutionary invention.
The oldest kind of computer is the abacus, used in China since the sixth century. In the seventeenth century an adding machine was invented, but the first large, modern computer was built in 1973. A few years later a computer could do 5,000 additions per second. Now the computations are so fast that they are measured in nanoseconds.
Today most computers are stored-program computers, that is, they have a memory. They are getting smaller and smaller, and computing faster and faster. Even in a large computer, the part that does the actual computing is about the size of the end of a fi
A. seconds
B. microseconds
C. milliseconds
D. nanoseconds
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