Checksum: 62231
Path: utzoo!utgpu!nishri
From: nishri@gpu.utcs.toronto.edu (Alex Nishri)
Date: Sun, 10-Jan-88 21:41:04 EST
Message-ID: <1988Jan10.214104.7965@gpu.utcs.toronto.edu>
Organization: University of Toronto Computing Services
Newsgroups: comp.ivideodisc
Subject: Re: CD (roms) question
References: <7813@eddie.MIT.EDU>
Reply-To: nishri@gpu.utcs.UUCP (Alex Nishri)

>What exactly is the capacity of a standard size CD, both in bytes and
>in playing time for music (assuming a standard speed)?

CD-A can have up to 72 minutes of audio, but due to molding problems toward the
outer edge of the disc, it is rare to see 60 minutes exceeded.  (The 'audio' is
actually in a spiral track which goes from the inside to the outside.)

CD-ROM, which uses the same disc, track, speed and other physical specifications
can store approximately 550 megabytes of data.  The actual amount quoted in
various sources varies both because the term 'megabytes' is not standard (is
it 1000000 bytes, or 1000 times 1024 bytes or is it 1024 times 1024 bytes?) and
because the amount of data you can store depends on the amount of error
correcting & detecting overhead you have.  If you are interested in the
technical details "CD-ROM Review" has covered them.  A good book to read is
the 1987 Bradley CD-ROM book.  Incidently, CD-ROM is one sided because CD-A
is.  CD-ROM gets its economies of scale by using the same glass mastering and
the same disc pressing plants as does CD-A.

Larger discs using the same technology are more expensive because they don't
enjoy the economies of scale.  A large optical disc can have one gigabyte worth
of data on one side.  There do exist two sided versions with two gigabytes worth
of information.

There also exists something called optical tape.  The same kind of technology
is used on a tape surface.  Capacity is measured in hundreds of gigabytes ...