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From: brazil@pawl18.pawl.rpi.edu (Timothy E. Onders)
Newsgroups: comp.arch,alt.next
Subject: Re: The NeXT Problem
Keywords: Curie point, local heating
Message-ID: <1490@imagine.PAWL.RPI.EDU>
Date: 21 Oct 88 14:04:06 GMT
References: <26435@ucbvax.BERKELEY.EDU> <7774@gryphon.CTS.COM> <9287@bigtex.cactus.org> <1359@cpoint.UUCP>
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Reply-To: brazil@pawl18.pawl.rpi.edu (Timothy E. Onders)
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The Cannon drive is not a true Optical drive. It is an optically enhanced
magnetic storage device. Through the use of lasers, the tracks can be made as
small as the width of the beam. The actual reading a writing is done with
a magnetic field, much the same as it is done in a normal hard drive. So
far, Tandy has been the only manufacturer to come close to a true erasable
optical media. Theirs seems to be based on phase change media, which changes
from clear to opaque and back depending on the power and wavelength of the
laser beam it is exposed to.
        As to fears of high temperatures erasing the disk, rest assured that
Cannon picked a material with a high enough curie point that you won't have
to worry too much about that. Besides, even if it is heated up to the point,
you would still need a magnetic field to damage the data.
        Although this is the first true market penetration for a read/write
optical-type media, the actuall technology was in use as early as 3 or 4
years ago. Then, as now, the phase change medium seems more promising, since
it allows for a lighter R/W head since it is not necessary to have a magnetic
coil, as well as the optics, not to mention the fact that, as Tandy suggested,
Phase change media could be read by present read-only devices, since the
data is stored in much the same way as on a conventional CD.

                                Timothy E. Onders
                                brazil@pawl.rpi.edu