Impact printers.

There are three main types of impact printers, dot matrix, daisy wheel and line printers.

Line Printers

Mainframe and mini computer systems often produce large amounts of output. An electricity board may, for example, need to print approaching two miles of bills each day. This requires something many times faster than the type of printer that would be attached to a PC.

Applications such as utility billing or payroll for a large firm use line printers. These are large, noisy and expensive. They can print from 600 to 1000 lines per minute but the quality if the output is poor and graphics are not possible. These large-scale printers are suitable for filling in account, invoice or payroll information on pre-printed stationery. They are only justified where large amounts of output are required. Line printers are impact printers - the characters are made by physical contact with ribbon and paper. This means that they can be used with multi-part stationery to produce second and third copies of the document. Multi-part stationery consists of several sheets. The second and other sheets are coated with a chemical that turns dark under pressure so that they take up an image of the characters formed on the top copy. One use of this would be to produce an invoice and delivery note in one print run, using two-part stationery.

Line printers use continuous stationery, which has sprocket holes in the side to allow it to be fed through the printer at high speed. The individual pages must be separated (burst) after printing.

Increasingly this type of output is being produced by large-scale laser printers. These are physically large printers which are capable of printing about 20 000 lines per minute. They are much quieter than a line printer but, because they are a non-impact printer, they cannot handle multi-part stationery. However a wider range of characters and graphics is available. Purchase and running costs are greater than for a line printer but the quality is greatly improved. Large-scale laser printers use continuous stationery.

Dot Matrix Printer

Characters are formed by pins, fired at a ribbon, producing dots on the paper. Using more and smaller pins produces higher resolution output. Two standards have emerged 9-pin and 24-pin. Dot matrix printers typically print up to 200 characters per second in draft mode. They usually have a slower higher resolution (NLQ - Near Letter Quality) mode. Graphics are possible as is colour with a special four colour ribbon.

The main advantages of dot matrix printers are that they are cheap to buy and run. They are an impact printer so they can be used with multi-part stationery. One application of dot matrix printers is in POS terminals where they are used to print the itemised receipt for a customer. Multi-part stationery is used and the second copy is retained at the till to provide an audit trail.

Daisy Wheel Printers

These are very old fashion but some are still in use. The printer has a single rotating head that has a whole character on each face they produce higher quality printing than other impact printers but do so much more slowly. Their big disadvantage is that they cannot produce images.