A local area network (LAN) is two or more computers directly linked within a small well-defined area such as a room, building, or group of closely placed buildings. A LAN may be made up of only microcomputers or any combination of microcomputers and large systems.

The computer network that connects the computers in the different parts of the same big city like metropolitan city may be referred to as Metropolitan Area Network (MAN).

Interest in local area networks is constantly growing due to following two developments
1.Developments in communication technology
2.The difference between a LAN and Development of powerful and user-friendly micro-computers

A multi-user system is that a LAN is made up of stand-alone computers whereas a multi-user system typically has one computer that is shared among two or more terminals.

A LAN usually consists of the following
1.Two or more computers
2.Peripheral devices such as printers and hard-disk drives
3.Software to control the operation of the computers or other devices connected to the LAN
4.Special cables, usually coaxial or fiber optic, to connect the computers and other devices
5.A plug-in board to handle the data transmissions.
6.A benefit of a LAN is the reduction of hardware costs because several computers and users can share peripheral devices such as laser printers, hard-disk drives, color plotters, and modems. Another advantage is the users can share data.

Ensuring the security and privacy of data are two concerns of LAN users. The LAN must get the data to its destination, transmit the data correctly, and prevent unauthorized users from gaining access to that data. These tasks are accomplished through both the hardware and LAN software.
They vary in the type and number of computers that can be connected, the speed at which data can be transferred, and the type of the software used to control the network. Some LANs require that all the computers be of a certain brand, while others allow a variety of brands to be connected. The number of computers in a LAN varies widely from smaller LANs that typically connect 2 to 25 computers, to large LANs that can connect as many as 10,000 computers.

The length of the cable connecting a computer to a LAN also varies depending on the LAN. Most LANs allow cables of about 1000 feet, but some allow cables of several miles to be used. The data transfer speeds range from several thousand bits per second to around 10 million bits per second. The programs that control the LANs also vary in the features they offer. Some programs allow the use of more than one operating system; others allow only one. On some LANs, file access is limited to one user at a time; on others, more than one user can access a file simultaneously.

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