Magnetic discs are based on ideas which were current 30 years ago in the recording industry. With a normal record you start playing on the outside run and the track goes round and round in a spiral to the centre. One problem with the cassettes is that you have to record all the information in a serial form. So if you have recorded say 8 programs, and want the information stored in the last one, you have got to start all the way from the beginning until you get to the information you want. One way of overcoming this setback is to take a normal LP-type record approach, where although you have got serial recording format, you have designated points called tracks. As there is a certain amount of random access, it is possible ...

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