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Digital Data Recording System

  • Magnetic tapes are used as the storage media in computers. There are two types:

    The incremental method of recording
    The synchronous method of recording

    In the incremental digital data recording system, the arrangement is such that for each digital character, to be recorded, the tape steps ahead. Therefore storing of data in this method is very slow. The data may also be discontinuously recorded. The characters of the data are equally and precisely spread along the length of the tape.

    In synchronous method of recording a start stop technique is used to run the tape. The tape moves no doubt at a constant speed of around 75 cm/s but it will be brought up to the speed and will then be stopped. During the run data inputs at precise rates, to the tune of tens of thousands of characters per second are recorded. A block of characters are recorded at one time.

    The different characters of data in a block are equally spaced over the length of the tape. The blocks of data are separated by erased portion of the tape termed as record gap. The coded combinations of one bit represent the characters of the data.  They occupy appropriate tracks over the width of the tape.

    The IBM accepted format of Non Return Zero technique is universally accepted for instrumentation recorders that use the magnetic tape as the media. In this method of recording data the tape will always be saturated either in positive or negative direction. The change in flux direction over the tape will indicate the '1' bit. No change in flux direction indicates a '0’ bit.

    Advantages of Digital Data Recording System:

    1. The accuracy will be high.
    2. The equipment required is simple.
    3. Digital recorders are not sensitive to tape speed.
    4. The output can be interfaced to a computer for further processing or control.

    Disadvantages of Digital Data Recording System:

    1. Rich quality of tape is required for recording.
    2. The analog information is to be converted in to the binary format.
    3. Analog to digital and digital to analog converters are required.
    4. Longer lengths of tape are required for storage of information.
    5. Only sequential recording and reproduction is possible.

    A recorder is an electromechanical instrument that produces a permanent record of one or more parameters as a function of another parameter.

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