Peripherals: Plotters and Communications devices and connectivity

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Plotters

A plotter is an output device for producing hard-copy of a drawing or design done on a computer. It consists of a flat surface on which a piece of paper can be fixed, together with a moving arm to which a pen is attached. The pen reproduces on the paper the design that has been built up on the computer screen. By automatically replacing the pen by another from a bank of pens at the side of the surface the plotter is able to produce multicoloured diagrams.

The price varies from a few hundred to several thousand pounds, the more expensive plotters permitting larger sheets of paper and working at higher speeds.

Communications devices and connectivity

For long-distance data communications over the telephone line, devices such as modems and fax machines are used. For computer communications within a building, network devices and cabling are required. All these are covered in Chapter 8.

Connectivity is the term applied to computer communi­cations and networking. In many offices today PCs are networked, giving the user the advantage of having a 'personal' computer while at the same time sharing files and data with other users. Indeed, most people work as mem­bers of a group rather than in isolation, and connected computers are therefore better able to meet the needs of the work situation. Some software, such as Lotus' Notes, is designed for work groups using networked computers.

We can list the advantages of having networked rather than stand-alone (i.e. unconnected) PCs as follows:

• Resources, such as hard disks and printers, can be shared.

• Software can be stored on a shared hard disk instead of being duplicated on every individual computer's disks.

• Files of data, stored on a shared hard disk, can be accessed by everyone.

• Electronic mail (i.e. memos and other messages that are typed on the screen but not printed, 'email' for short) can be passed from one machine to another, providing a fast and low-cost messaging system.

• Incompatible hardware, such as PCs and Macs, can be linked by means of the network and files passed between them.

• Data is less likely to be accidentally erased and lost, as formal housekeeping procedures will normally be insti­tuted, under the control of the network manager, for carrying out tasks such as making regular backups.

So besides allowing office staff to share resources and services, networking means that they can also share data­ bases, diaries, and other sources of information, and elec­tronic mail (messages) can be passed between them.

In a network there must be a 'host' computer. This is the file server, so called because it holds, on its hard disk, the files used by the other computers on the network. (The file server may be able to also act as an ordinary networked computer or workstation, though the person using it may find that some operations are slowed down as part of its processing resources are servicing the network.) The other computers connected to the network may be called clients, terminals, or stations.

So far as personal computers are concerned, the most common type of network is the local area network, or LAN. In this, the various computers and other equipment are linked together by a single long coaxial cable laid around the site. Besides this cabling, each must normally have a network card containing special network circuitry installed inside its casing. For more detail on networking, see page 178.

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