计算机输入输出Computer’sInputandOutput英文资料中英文翻译中文.doc

Computer’s Input and Output（计算机输入输出） Accessing a Computer A computer is a machine that processes data into information. Unless some human being needs the information, there is no point to processing the data. Without data, there are nothing to process. Input and output devices provide a means for people to access a computer. In this chapter, we’ll consider a number of input and output devices and media, and then show how they are physically linked to a computer. Basic I/O Keyboards and Display Screens The basic input device on most small computer systems is a key-board. As characters are typed, they are stored in main memory, and then copied from memory to the basic output device, a display screen. In effect, the screen, often called a monitor, serves as a window on main memory, allowing the user to view its contents. Several different types of displays are available. Some shoe white characters against a black background; options include green and amber screens. Color monitors display characters, charts, pictures, and disgrams in color. Standard television sets are sometimes used as inexpensive display devices, but, because the clarity of a televising signal suffers when small elements (such as letters and digits ) are displayed, real computer monitors produce a much sharper image. Printers The image displayed on a screen is temporary; it fades as soon as the power is cut. By routing the output to a printer, a permanent copy (called a hard copy) is obtained. Dot matrix printers form characters from patterns of dots; they are inexpensive, but the output can be difficult to read. Letter-quality printers type complete, solid characters, and produce a clean, sharp impression. More exotic techniques form images by spraying ink or by selectively buming (carbonizing) the surface of the paper. Graphice Graphic Output Computers are not limited to displaying characters; graphic output is possible, too. Remember that a computer’s output comes from main memory. Thus, if a gra