| We have mentioned mass storage in passing
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| | particles. This allowed the heads to be
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| previously, in the history of the
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| | moved closer together, and more data to
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| computer series. The term mass storage
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| | be held around the drum, and on more
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| is applied to a group of media, including
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| | tracks. Speed could also be increased,
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| drums magnetic tape and disks. It has
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| | improving access times.Another
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| the advantage of high capacity, but slow
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| | application of the drum, the Fastrand
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| access times, in comparison to RAM.For
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| | from the Sperry Univac company, had two
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| this reason, it is used as a long term
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| | horizontally mounted drums of
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| (computer time), or back-up medium. The
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| | approximately 2ft diameter and about 8ft
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| current data and programs the processor
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| | long. A beam mounted between the drums
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| is working on are kept immediately
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| | and carrying read/write heads was able to
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| accessible in main memory, RAM, and they
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| | move horizontally, so increasing the
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| are replenished as required from mass
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| | number of tracks each head could address.
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| storage. At the same time, programs and
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| | This system was used extensively on
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| data which are no longer required to be
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| | Univac computers of various sizes
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| instantly available are written out to
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| | starting in the 1960s. The capacity was
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| mass storage.MAGNETIC DRUM STORAGEEarly
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| | equivalent to around 100MBThe drums
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| computers used drums for both main memory
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| | rotated in opposite directions, at 880
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| and mass storage, but with the
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| | RPM, and the beam was driven by a 'voice
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| development of core memory in the 1950s,
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| | coil'. The voice coil was named thus as
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| drums were used as mass storage, backing
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| | it resembled the voice coil of a
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| up the core memory. This was necessary
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| | loudspeaker. This works by passing an
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| as core was expensive, being hand made, a
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| | analog proportional current, representing
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| typical capacity was 28Kbits.A typical
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| | music, or speech, from an amplifier. The
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| drum storage unit used a magnetic
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| | loudspeaker cone, attached to the voice
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| recording medium coated on a vertical
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| | coil, and in the presence of a permanent
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| cylindrical drum approximately 10in. in
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| | magnet, is driven by the electromagnetic
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| diameter, and about 20in. high. The drum
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| | action, and converts the current into
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| rotated at a speed of around 430, later
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| | sound waves.In the case of the fastrand,
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| 880 and 1760 rpm. Data was written to
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| | the voice coil was fixed, and a section
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| and read from this drum by a series of
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| | of the beam passed through it. A servo
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| read/write heads which almost touched the
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| | system drove the current in the coil to
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| surface of the drum, held away by air
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| | move the beam to the desired address.Also
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| pressure in a similar manner to an
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| | mounted between the drums, not on the
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| aircraft wing. These were known as
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| | moving beam were a number of 'fixed
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| 'flying heads'.The data was written to
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| | heads'. These provided fast access to
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| the drum by passing a current through a
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| | data, as they didn't need to wait for the
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| coil on a C-shaped electromagnet, the gap
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| | beam to move to access the data. They
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| between the poles of the magnet being
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| | were typically used for the 'boot block'
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| aligned close to the drum. Thus the
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| | to give a fast start.Problems with all
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| circular track around the drum carried
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| | drums occurred when the head contacted
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| sequentially written data (serial).The
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| | the magnetic surface. A 'hit' might
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| data was located by referring to a once
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| | cause the data to be lost at that point
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| per revolution pulse, generated by a mark
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| | but was a warning of an impending 'crash'
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| on the the drum, and by addressing a
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| | - a catastrophic event. This would
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| particular head. Reading was carried out
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| | entail recovering bits of read/write
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| by addressing the required head, or
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| | head, repairing the drum surface, then
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| track, and the distance around the drum.
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| | replacing and re-aligning the head.
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| A current was generated in the coil on
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| | Cabinets were pressurised to keep out
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| the read/write head, and data passed back
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| | dust, to minimise this happening.In part
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| to the system.As technology improved, the
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| | 2 we look at magnetic disks.Tony is an
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| heads were made with smaller gaps, and
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| | experienced computer engineer.
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| the magnetic coating used finer
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