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2 Local Area Networks

Computers within a department or campus often communicate over a local area network, or LAN (see Figure 1). These networks are fairly small, in terms of physical distances, usually limited to a single building. The three basic categories of equipment that are found in a local network are workstations, servers, and gateways.

Users access networks through terminals and workstations. A terminal is simply an I/O device; the only processing it does is limited to presenting information for display on the screen. Simple (``dumb'') terminals do little or no formatting, so everything that is displayed is arranged by a computer system and every keystroke is passed back to the computer. For example, if you make a mistake while typing a line and hit the backspace key, a terminal just sends the keystroke to the computer you are using. The computer will update an internal buffer and send the terminal a command that will cause it to move the cursor to the left by one space. Until a few years ago terminals were connected directly to computers, but now it is common for them to be connected to a communications server, as shown in Figure 1. The server then uses the local network to connect the terminal to any machine on the network, giving users more flexibility.

Figure 1: Local Area Network.