LAN or Local Area Network is a computer network that connects computers within a confined geographical area. There remains a server that controls all the other computers which are termed as clients. For a small LAN a NOS or Network Operating System is not a necessary. But when there are more clients we need a dedicated server installed with NOS Network Operating System. Windows 2003 Server is the latest NOS from Microsoft. Some remarkable names include LINUX, NOVEL NETWAREW, UNIX, MAC OS etc. The clients are less powerful computers, sometimes diskless and sometimes only with a floppy drive. Some clients are used only as terminals which are used only to display what comes from the server. However in a simple network sometimes Peer to Peer structure is applied. In a peer to peer network the clients can be used as servers to access data from other machines. But in a large network it is not ideal. Only a dedicated server can offer you high transmission speed and better performance.

The usefulness of a LAN is that it enables to control a huge number of machines from a single machine- the server. You can use the server to distribute and collect data, to control access of the client machines, to divide the clients into different domains and sub-domains, to store data and many more things.

Routers are network devices that determine the route through which data is transmitted. In a LAN (Local Area Network) when some data is transferred from one machine to another, it becomes necessary to determine the route. This is what a router does according to its internal routing table. When some data is to be sent from one machine to another, it is divided into some packets. The size and nature of the packets vary according to different routing protocols such as IP, IPX. Some routers support more than one protocol. Usually routers are specialized computers. However, sometimes routing technologies are found implemented in some NOS (Network Operating System) s like NetWare.