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Information (audio, video, or data) to be recorded magnetically is first encoded into a sequence of time-varying electrical signals which are used to drive a writing head, the magnetic field of which creates, on the moving tape or disk, a spatially varying pattern of magnetization. The reading process uses another head (or the same head) to reconvert this magnetization pattern into time-varying electrical signals that can be amplified and used to drive a loudspeaker, or a TV receiver, or feed data to a computer. Two methods of encoding the information are used; analog and digital. In analog recording, as the adjective suggests, the pattern of magnetization on the recording medium should be a precise analog of the incoming stream of information and the signal obtained on reading should be an exact reproduction of the original. Digital recording involves first converting the information into a sequence of ones and zeros which can then be recorded as a sequence of regions of opposite magnetization. Analog recording has been widely used to store audio and video information while digital recording was used for data recording. This picture is changing and digital recording is now being used increasingly in audio and video recording principally because errors can be corrected dynamically so that the original information can be reconstructed and copied repeatedly and with great fidelity. Whether the recording method used is analog or digital, similar though not identical properties are required of the recording materials and so the distinction between the two methods will not be pursued further.