COMPONENTS OF LAN

LAN is made up of hardware as well as software components. Hardware consists of interface cards in all the machines and cables that tie them together. The software includes the drivers for all peripherals and network O.S. that manages the network. Some of important components are:-

Server

We have already explained earlier what exactly a file server is. There is more to be said about it. However, A file server can be dedicated or non-dedicated. A dedicated server only allows access to files stored in its hard disk drive. A non-dedicated server, on the other hand, can be used also as a stand-alone PC, while in the background, ii serves the LAN.

One interesting new feature that has emerged today is that a LAN can give more than one file server. One of these servers can be used as backup. Which means it will store copies of every file on the other servers and can become the primary server in case the actual primary server fails. This is known as apparent redundancy.

The future servers are going to be much more powerful than today's file servers. In fact, they have; already emerged. One of them is called the Communication Server . A communications server is an extraordinary powerful product. Any PC attached to this server can communicate directly to any large computer like a minicomputer or a mainframe which is outside the LAN. In fact, it will work exactly as a terminal attached to that computer. The results of the work performed using this PC can be used in the same manner as would use any PC's output.

Another powerful server that has arrived is called the Database Server. This allows our PC to access the superior database processing capabilities of large computers. Both the communications server and the database server can work hand in hand with the LAN software at the same time.

Adapters for Interface

Now that we know that two major components of a LAN are a terminal and a file server, what we need to know now is how they communicate. What exactly is the medium through which information is transmitted between them?

For connecting one PC to a LAN system, we have to use a special interface adapter card. These cards are plugged into the expansion slots just like other cards. These cards translate signals received from the CPU and send them across the network. The LAN software manages these cards.

The popular Network Interface Cards (NICs) in use today are Ethernet, ARCnet, Token-Ring and FDDI (Fibre Distributed Data Interface).

Connecting the Network: Cabling

Just plugging the cards into the expansion slots is not enough, really. Each PC on the LAN will have an adapter card. The connection is net made, however, until all the PCs are linked through a network of cables. Various types of cables are available for networking.

The ones used most frequently are twisted-pair cables and coaxial cables. A twisted-pair cable consists of pairs of copper wires. These are twisted together to enable cancelling out noise and external disturbance to the signal that they carry. Unlike the twisted-pair cable, the coaxial cable contains only one wire. Special insulation is provided to protect this wire. This cable is more efficient, fast and carries more information than the twisted pair cable. It is also, hence, more expensive than the twisted pair cable. A point to be noted is that these cables carry signals in bursts of electricity.

A third type of cable is also available. It is the Fiber-optic cable. This contains a very thin (as thin as the human hair) cable made of optical fiber. This cable transmits much more data and mush faster too. This is because this cable caries signals in light pulses {light, as in ray of light). Light, as we all know is the fastest entity and very naturally, will be faster than electricity. This type of cable is very expensive, however, and presently only telephone' companies and large government organizations which need and can afford it are using it.

Another possible alternative that is emerging is actually wireless. There will be no wires here and data will be transmitted using radio waves or infrared rays. Government clearance may be required before they can be used.

WorkStation

A workstation has its own local Operating system depending on Machine Type; workstations can be DOS-based PCs, Application-Mac's running system. A workstation's main Job is to execute Program Files retrieved from networks. With advent of network based client - server computer the role of server has changed. In this distributed processing environment, processing burden is shared by server and workstation.

Shared Resources

Shared resources include storage devices attached to server, optical disk drives, printers, plotters, modems and other equipment that can be used by everyone on network sharing hardware not only reduces cost by making duplicate purchases redundant, but. LAN also can access a wide variety of equipment.