InformationWeek SMB TechEncyclopedia

(Local Area Network) A communications network that serves users within a confined geographical area. The "clients" are the user's workstations typically running Windows, although Mac and Linux clients are also used. The "servers" hold programs and data that are shared by the clients. Servers come in a wide range of sizes from Intel-based servers to mainframes. Printers can also be connected to the network and shared (see print server).

Thick and Thin Clients
In a LAN, the client machines are mostly Windows-based PCs that contain their own applications. These "thick" clients are the norm; however, some companies use "thin" clients, which are stripped-down machines. Some are diskless and floppy-only workstations that retrieve all software and data from the server. Windows terminals are also used, which are Windows PCs that act like input/output terminals. They perform no business processing and display only what comes from a central server. See thin client and Windows terminal.

The Network OS
The controlling software in a LAN is the network operating system in the server (Windows, Mac OS, Linux, Unix, NetWare). A component part resides in each client and allows the application to read and write data from the server as if it were on the local machine.

     Client workstations can also function as a server, allowing users access to data on another user's machine. These peer-to-peer networks are often simpler to install and manage, but dedicated servers provide better performance and handle higher transaction volume. In large networks, multiple, dedicated servers are used.

The Transport
Data transfer over the network is managed by a transport protocol such as TCP/IP or IPX. The physical transmission is performed by the access method, almost exclusively Ethernet, which is on the motherboard or in the network adapter cards (NICs) plugged into the machines. The actual communications path is the twisted pair or optical fiber cable that interconnects each network adapter. See WAN, TCP/IP, Ethernet and client/server.




Clients and Servers in a LAN
This illustration shows one server for each type of service on a LAN. In practice, several functions can be combined in one machine and, for large volumes, multiple machines can be used to balance the traffic for the same service. For example, a large Internet Web site is often made up of several Web servers.










The Software in a Network Client
This shows the various software components that reside in a user's client workstation in a network.




The Software in a Network Server
This shows the network operating system and various system software components in a network server.