计算机专业英语
Passage(A)
Characteristics of Clients and Servers
The term client and server refer to the two applications involved in a communication. The application that actively initiates contact is called a client, while the application that passively waits for contact is called a server.
Confusion sometimes arises over the term server. Formally, the term refers to a program that waits passively for communication, and not to the computer on which executes. However, when a computer is dedicated to running one or more server programs, the computer itself is sometimes (incorrectly) called a server. Hardware venders contribute to the confusion because they classify computers that have fast CPUs, large memories, and powerful operating systems as server machines.
We adhere to scientifically accurate terminology and use the term server to refer to the running program and not the computer. The term server-class computer refers to a powerful computer used to run server software.
Information can pass in either or both directions between a client and a server. Typically, a client sends a request to a server, and the server returns a response to the client. In some cases, a client sends a series of requests and the server issues a series of responses (e.g., a database client might allow a user to look up more than one item at a time). In other cases, the server provides continuous output without any request -- as soon as the client contacts the server, the server begins sending data (e.g., a local weather server might send continuous weather report With updated temperature and barometric pressure).
It is important to understand that servers can accept incoming information as well as deliver outgoing information. For example, most file servers are configured to export a set of files to clients, That is, a client sends a request that contains a file name, and the server responses by sending a copy of the file. However, a file server can also be configured to impo
