632 Chapter 21
Computers are the main end use of DVD at present, but DVD drives to replace
videocassette players are already widely available. The spread of DVD as a replacement
for VCR, however, is not likely to spread widely until the recording version reaches an
acceptable price level. Surveys have shown repeatedly that the most common use for VCRs
in the United Kingdom is to record TV programs either when the viewer is not at home or
when two interesting programs are being broadcast at the same time. Use of DVD simply
to play prerecorded discs is very restrictive—I cannot think of more than a handful of fi lms
I would ever want to see again, and some of my own videotapes have not been played since
the day I recorded them. This is mainly a United Kingdom attitude, and the laser disc that
was rejected in the United Kingdom has survived up until now in other countries.
● With the primary markets of computers and fi lm viewing now being supplied, we
are waiting for a standardized DVD format for audio that reportedly will allow up
to 17 h of CD quality to be stored on a single disc.DVD offers so much more storage space than CD that the options it allows are more than
most users can cope with at fi rst. A single-layer disc can store just over 2 h of digital
video signals at a higher quality than is possible using VCR (which relies on considerable
bandwidth reduction). More than one layer of CD recording can be placed on a disc,
however, because the layers are transparent, and by altering the focus of the reading laser,
it is not technically diffi cult to read either of two superimposed layers that are only a
fraction of a millimeter apart.
By making two-layer DVDs the recording time can be doubled, and by adding double-
sided recording it can be doubled again to 8 h of video. The discs can contain up to eight
audio tracks, each using up to eight channels, so that fi lms can contain soundtracks in
more than one language and cater for surround sound systems.
Figure 21.4 : The rear of an APEX AD 600A DVD player that also plays CDs and MP3 fi les,
priced in the United States at about $150.