Computers are connected via hardware (cables) and software (communication protocols). Computers that are physically close are connected via local area networks (LANs). If the computers have access to computers outside the local network, they typically go through a computer set up as a gateway. This gateway computer (usually one of the fastest ones on the network), forwards and receives messages for all the computers on the local network from and to the "outside". Larger networks are commonly called wide area networks (WANs).
A communications link is the physical medium used for data transmission. Common types of links include
The range of frequencies a device can handle is called its bandwidth. The higher the bandwidth, the more information can be sent across the line in a given amount of time.
A protocol is a set of rules for the exchange of data between a terminal and a computer or between two computers. Standard protocols are important for without them, information could not be reliably communicated between computers.
The physical layout of a local area network is called a topology. A variety of network topologies are common including star, ring, and bus.
A client/server model is contrasted with a file server below.
Client/server model - The client asks for information and the server does some processing to produce the results and give them to the client. There are typically many, many clients that use the same server. The clients primarily display the results, including possibly graphics and/or sound, on the local machine.
File server - A file server is a large computer with fast input/output capability and a huge amount of disk space. The file server keeps the "original" copies of files for other machines, and "serves" them when requested to do so. It does not process the files, but produces a copy when asked. This means that you can log into any one of a group of computers and still have access to the same files. You may edit the files locally, but when you save the files, they are saved back on the file server's disk, so they are available in the future from the server.
You have used servers whenever you access web pages! Also, your email is stored on a machine called your mail server. It takes both hardware and software to perform the duties of a server.
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