计算机英语sectionA课文及对应中文翻译..doc

第七单元 Telecommunications enables people to send and receive personal messages across town, between countries, and to and from outer space. It also provides the key medium for news, data, information and entertainment. When a signal reaches its destination, the device on the receiving end converts the electronic signal back into an understandable message, such as sound over a telephone, moving images on a television, or words and pictures on a computer screen. 电信使世界各地的人们得以互相联系，即刻获 取信息，并从边远地区实施通信。电信通常涉及一个信息发送者和一个或多个接收者，他们通过电话系统等把信息从一地发送到另一地的技术相联系。电信设备将不同类型的信息，如声音和图像，转换成电子信号。然后，这些信号就可以通过电话 线或无线电波等媒介进行发送。信号到达目的地后，接收端的设备将电子信号转换 回可以理解的信息，如电话中的声音、电视上的活动图像或计算机屏幕上的文字和 图片。电信使人们能够在城镇不同地方、国家之间以及向外层空间和从外层空间发送和接收个人信息。电信也为新闻、数据、信息和娱乐提供了关键的媒介。 Telecommunications messages can be sent in a variety of ways and by a wide range of devices. The messages can be sent from one sender to a single receiver (point-to-point) or from one sender to many receivers (point-to-multipoint). Personal communications, such as a telephone conversation between two people or a facsimile (fax) message, usually involve point-to-point transmission. Point-to-multipoint telecommunications, often called broadcasts, provide the basis for commercial radio and television programming. 电信信息可通过各种方式和设备发送。信息可由一个发送者发送给一个接收者（点对点）， 或者由一个发送者发送给多个接收者（点对多点）。个人通信，如两个人之间的电话对话或传真信息，通常涉及点对点的传输。通常称为广播的点对多点电信传输，为商业无线电和电视节目播送提供了基础。 Telecommunications begin with messages that are converted into electronic signals. The signals are then sent over a medium to a receiver, where they are decoded back into a form that the person receiving the message can understand. There are a variety of ways to create and decode signals, and many different ways to transmit signals. 电信以信息转换为电子信号为 开端。然后，这些信号通过媒介发送到接收机，并在那里解码，恢复为接收信息的 人能够理解的形式。有各种方法可以生成并解译信号，也有许多不同方法可以传输 信号。 Devices such as the telegraph and telephone relay messages by creating modulated electrical impulses, or impulses that change in a systematic way. These impulses are then sent by wires