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A LAN (Local Area Network) is a high-speed communication system that lets different types of computers communicate and share data within a building or room. A LAN's main use is to let the attached computers have access to shared files and printers. The difference between a LAN and a minicomputer system is that with a minicomputer system all the processing is done by the minicomputer running the programs. The workstations attached to the minicomputer are only used as input and output devices for entering data and displaying results. With a LAN, the programs running on the workstation do the processing. This allows each user's computer to run its own software and process information independently. A LAN is made up of a combination of client computers, printers, network cards, and network cables to attach them all together.
There are two major types of Local Area Networks: Peer-to-Peer and Client/Server. In a Peer-to-Peer network, a user's workstation is both a client and a server. Users can share files on their hard disks with other users on the network without going through a file server. Every computer on the network has equal access. Advantages to this type of network are that it is easy to set up, and very inexpensive. Disadvantages are that there is no dedicated file server, and there is limited security.
Client/Server networks, on the other hand, have a dedicated server that provides resource sharing for the whole network such as database access, printer sharing, and file storage. One advantage to Client/Server networks is the security. Each user must have his own user name and password to access the server.
The term client is used to describe a computer that accesses network services such as files and printers. Client computers can vary, depending on the applications required by the user, to best meet each user's needs. Along with meeting the hardware requirements of the software, each client computer must have a network card in order to attach it to the cable system.
A server is a computer that provides network services that client computers can access. A file server allows multiple client computers to access and save data on the servers file system.
Shared access to a high-speed printer is important in a local area network. The advantages of placing a printer on a network are cost savings, increased workspace and printer selection depending on application needs. Printers can be connected to a network in one of three ways:
- Attached to the server - Local Printer
- Attached to a client computer - Remote Printer
- Attached to the network cable - Network Printer
Printers are not commonly attached to the server because the server computer is usually located in a separate locked room. Attaching a printer directly to client computers provides easy access but gives slower performance. Attaching a printer directly to the network provides better performance and reliability but is more expensive, because the printer then needs a network card.
A network cable system consists of the cable media, which is the physical wire that is used to transfer data between network computers, and the topology, which is the physical layout of the cables used to connect 
network devices.
Coaxial cable is commonly used with cable television systems as well as local area networks. It consists of a central conductor covered by a wire mesh shield. The advantages of coaxial cable are high-speed transmission and good protection against electronic interference. Disadvantages like high cost bulk make it not a common choice for larger networks.
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Unshielded Twisted-Pair (UTP) cables are commonly used with telephone systems and local area networks. Advantages are that it is relatively inexpensive, easy to install, and has transmission speeds of up to 100 Mbs. |
The disadvantage of UTP cable is it is susceptible to electrical interference from outside sources, such as fluorescent lights.
The advantage of Shielded Twisted-Pair (STP) cable is it reduces the effects of outside interference by covering the twisted-pair cables in a wire mesh shield. |
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Disadvantages are high cost, bulk, as well as the decrease of speed and distance signals can travel due to the addition of the wire mesh shield.
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Fiber-optic cable consists of glass or plastic fibers surrounded by a durable outer jacket. It is very expensive, but provides extremely high transmission rates over long distances with little interference. |
Star topology consists of a central hub attached to each computer on a network with cable segments. The hub distributes signals coming from one computer to the others on the networks. |
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Linear bus topology consists of coaxial cable that runs from one computer to the next with a terminator at each end. The terminators stop electrical signals when they reach the ends of the cable; this prevents interference.
While star and linear bus topologies are most commonly used, there is also ring topology. Ring topology is similar to bus topology except that the ends of the cables are connected.
The Network Interface Card (NIC) is responsible for transmitting data in packets. Each packet contains the address of the receiving computer's network card, just like the mailing address on a letter. There are many manufacturers of network NIC's but the most commonly used are Token Ring, Ethernet, 10BASET, and 100BASET. Each has a different method of transmitting data. |
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Before LANs, companies used dumb terminals to connect to a mainframe that allowed users to share printers and information. The client computers were only able to request and display data from the mainframe; they couldn't do any processing and had no storage capabilities. LANs now allow users to share files, applications, printers and modems. It's amazing what advances in technology have enabled us to do!
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