Peripherals

Terms that are often used when people talk about computers are hardware, software and peripherals.

The computer hardware can best be described as the actual parts that go together to make up the computer such as wires, switches, electronic circuits, microprocessors and anything else that is involved in the working parts.

Software refers to the programs that are input into the computer. Disks and cassettes are often referred to as software once they have computer programs on them but they are really peripherals.

The peripherals of the computer are the devices for input, output or storage of data and include the keyboard, visual display unit, cassettes, disk drives and printers. The VDU is also known as the monitor and the program and the results of the processing can be seen on this, as well as the data entered. The printer will produce the print-out of the results of the processing. This is often referred to as hard copy.

The highest quality of printer available is the daisy wheel. This consists of a wheel with flexible stems radiating from the centre. The letters are well-defined and can be read clearly. The printer moves bi-directionally printing both ways from left to right and then right to left. Remember that what is to be printed already exists in the memory of the computer and the daisy wheel does not have to type in sequence as would be expected from a human brain. The carriage therefore need not waste time returning at the end of each line.

The dot matrix is usually faster than the daisy wheel. The printer has a print head consisting of a row of needles. This moves speedily over the place where a letter has to be printed using dots to make up the letter. The needles print on to a special typewriter ribbon. The quality of print-out is not of a very high standard and would not generally be used at high business levels. However, it is often used for the production of rough drafts. Characters of different sizes can be built up with dot-matrix printers and some may have two-colour ribbons.

An ink-jet printer forms dot matrix characters by applying ejected droplets of ink, vibrated at an appropriate frequency, towards a special absorbent paper. A charged electrode is placed near the jet, so that each droplet carries a charge. By a special electrostatic technique the ink drops can be directed to particular parts of the paper. The printers use information that is stored digitally.

Thermal printers require a heat sensitive paper which is marked by a heated needle-like writing implement known as a stylus.

Laser printers are very fast and can use different sizes of paper. Since they are non-impact printers they are very quiet and can produce good graphics. The laser printer works by beaming a laser on to an electrically charged drum which creates an invisible image on the drum, revealed when a special substance, called toner, is poured over it. When the paper is brought into contact with the drum, the image melts on to the paper as it is heated.

The keyboard is where the data, or information, is input into the computer. It is usually arranged like an ordinary typewriter keyboard with a number of other keys added which carry out special functions.

Some computer programs display what are called icons on the computer screen. The icons may represent items of furniture in an office for instance. The user is able to instruct the computer by the use of a tiny moveable device known as a mouse which is connected to the computer by a cable and can be moved about the top of a desk. The desk represents the VDU screen and as the mouse moves about, it moves with the short bright line, known as the cursor, on the screen.

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