编辑：电脑专家网  www.pc10000.com

Client/Server Concepts

A client computer initiates a service request. A server computer waits to reply, kind of like a person who waits to answer the phone so you can make airline reservations.

A client program can be directed by a human being (at a screen, keyboard, and mouse), or it can run automatically.

A server is a program that knows a protocol for communication (see below), but often doesn't know much about networking -- it just exchanges bytes of information with the client, a back-and-forth conversation that might be human-readable ASCII, or binary code; kind of like when you call someone to make a reservation, and they don't know how the phone system works, just how to use the telephone to talk with you.

It's entirely possible for the client and server programs to be on the same computer, as well as on two different computers connected by a network. The client/server model blurs the boundaries between computers, to where "the network IS the computer."

Once a virtual connection is established between a client and server, the two systems are peers, but the client/server asymmetry usually continues through the protocol; just like when you're done dialing someone, it doesn't matter much who placed the call, you can talk to each other as equals, though quite often the caller and the callee have very different roles. (With phone calls the caller usually pays for any long distance charges, but there's usually no equivalent in network connections.)