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NETWORK TOPOLOGIES and the WEB
There is a saying that "The whole is greater than the sum of its parts." This is certainly true of microcomputers.
Individually, they are useful. but when linked into a local area network (LAN). they become even more so. Local area networks
can connect computers within a single building or in several nearby buildings, on a college campus. for instance. It is estimated
more than one hundred million computers are already connected into local area networks, and that number is growing. There
are two primary reasons for connecting computers into local area networks.
The computers can share expensive peripherals like plotters. Laser printers, and hard disk drives. Where there are only
a few computers this can also be accomplished by switches that switch a printer or other device between the computers.
The computers can communicate with each other, and users can exchange Information and electronic mall.
Local area networks are created by connecting microcomputers, printers, and hard disks with wires or cables. Microcomputers
connected into a network operate together as equals. Each microcomputer has its own computational ability, so it can function
either alone or as part of the network. LANs differ from multiuser systems where dumb terminals, or microcomputers that act
like dumb terminals. are connected to a central computer. In a multiuser system. the dumb terminal can draw only on the resources
in the main computer: it cannot run its own programs. In a LAN. the computers can be regular microcomputers or diskless workstations,
which are microcomputers without disk drives. All the programs it runs and all the data files it saves are stored on the network's
hard disk drive. Diskless workstations are more secure than computers with disk drives. For example, users cannot illegally
copy program or data files that are stored on the network's hard disk.
Many users want to call computers that are not connected into a local network. To do so, they dial up these computers
using their modems, which are connected to the telephone lines. These telephone lines are also referred to as a WIDE AREA
NETWORK Using this network, you can call other computers, information services like CompuServe, or bulletin boards set up
by companies or Individual users. The computer that you call is the host computer. The host computer can be the computer that
runs the information service, a mainframe or minicomputer, a PC running a bulletin board, or another computer running a communications
program.
You can communicate with thousands of computers through telecommunications. They fall into four classes:
~ Information services that offer a varied of databases and other services. You must subscribe to the service and are
then billed for the time you are connected to the service.
~ Electronic mall services are available for sending messages and mail. Your message is stored by the computer and then
forwarded to the person it is addressed to when he or she logs on (signs on) to the service.
~ Bulletin boards are set up by individuals or groups. You can call them without charge.
~ Private wide area networks set up by corporations are open only to members of the company.
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