At its core, a network is simply two (or more) connected computers. Computers can be connected with cables or telephone lines, or they can connect wirelessly with radio waves, fiber-optic lines, or even infrared signals. When computers are able to communicate, they can work together in a variety of ways: by sharing their resources with each other, by distributing the workload of a particular task, or by exchanging messages. Today, the most widely used network is the Internet. This book examines in detail how computers on a network communicate; what functions they perform; and how to go about building, operating, and maintaining them.
The original model for collaborative computing was to have a single large computer connected to a series of terminals, each of which would service a different user. This was called time sharing because the computer divided its processor clock cycles among the terminals. Using this arrangement, the terminals were simply communications devices; they accepted input from users through a keyboard and sent it to the computer. When the computer returned a result, the terminal displayed it on a screen or printed it on paper.These terminals were sometimes called dumb terminals because they didn’t perform any calculations on their own. The terminals communicated with the main computer, never with each other.