LED's and Buzzers

Light emitting diodes are often used to display the status of a system or in control applications. One example is the use of LED's on a keyboard to indicate the status of the Number Lock and Caps lock keys. LED's require little power, do not produce light by heating and so do not get hot, are cheap to buy and have a long life.

Buzzers are useful to alert the user to some event - such as an error condition. They are used in POS terminals to indicate that a bar code has been correctly read.

Computer Output on Microform (COM)

Photographic film is used as the output medium in this method of output. The output device exposes the image onto the film which is then developed to provide a permanent record. Two forms of film are use. Microfilm which looks like 35 mm camera film and Microfiche which is about 6 inches by 4 inches. A single microfiche sheet will contain the equivalent of 200 A4 pages.

The images are too small to be read unaided so a special reading device is used to magnify the image and project it onto a screen.

The principal advantage of COM is that it compresses a large amount of data into a small space. Catalogues and reference material are often output to microfilm or microfiche although increasingly this type of information is output to CD-ROM.

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