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Video on Demand The
product is based on the ordinary magnetic
disk drives,
known also as 'hard
disks' or simply as 'drives',
made in large numbers and types (exceeding
100 million
units annually) by many firms, and used by all PC's as a peripheral
memory. All drives are interchangeable
and plugable,
cheap but reliable, each an autonomous player,
and small. They access their
contents rapidly,
have a huge capacity, and are sold by innumerable
distributors. A
selected drive type will be modified to store TV
programs instead of computer data. The programs will
be movies,
documentaries, educational
works, sports events,
etc. (all herein named "movies").
Storing will be done with
a new technique that annuls tracking accuracy
needs, plays the contents continuously,
and if needed raises the capacity with thinner heads. With
a drive's capacity
and data rate exceeding the video needs,
the movies will be
multiplexed field after field
in a set
of 6 or more per
track, the total sets holding
6 or more movies of 2-hr
maximum duration each movie.
Thus, a 13 GB
drive, only
4.1x10x15 cm in size, will
store more than 6 movies
of 12-hr playing time
and will simultaneously
replay all, each on a separate line. In
addition, since
large-capacity drives use many disks
and often 20 or more
heads, all stepping together from track to track,
they will be provided with
a separate read/write amplifier per head instead of only one in normal use.
Activating all heads in playback divides each movie into an equal number of
evenly spaced entries or "epochs", unlike tape or CD players having a
single head, and in essence eliminates the queue: With data re-circulation,
whereby heads step serially from track to track and at the last track return to
the first to repeat the process endlessly, any movie is seen from its start (or
other epoch) by a simple connection to the entry nearest the wanted point. Thus
the queue will at most equal the playing time interval between heads. Multiplexing
and using all heads lets a drive store and replay more than one movie per full sequence
of its tracks in the case of pieces shorter than 2-hr. Since neither a piece's
length nor its place in the track sequence affects the queue, for it never
exceeds the time between heads, any mix of long or short pieces in a succession
lasting 2-hr will also be named a "movie" for brevity. A striking
feature is that a drive's entire 12-hr in duration contents can be updated in
only 3 minutes from a
master drive with all 20
heads activated and using 20
lines. This is 120
times better compared to tape players copying at their fastest and eliminates
the existing bottleneck in video
replication. A
novel, then, and very powerful product is realized as a modular system made of
many identical and modestly modified drives, each practically a complete,
independent and miniature player. The drives (or "Modules") will be
housed in a small cabinet forming with the usual power supplies, etc. the VOD
installation (or "System").
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