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Path: utzoo!watmath!clyde!cuae2!ihnp4!houxm!hjuxa!catnip!ben
From: ben@catnip.UUCP
Newsgroups: comp.periphs
Subject: Re: CD to CD-ROM conversion
Message-ID: <431@catnip.UUCP>
Date: Sun, 14-Dec-86 17:05:31 EST
Article-I.D.: catnip.431
Posted: Sun Dec 14 17:05:31 1986
Date-Received: Tue, 16-Dec-86 18:50:31 EST
References: <1787@jade.BERKELEY.EDU>
Reply-To: ben@catnip.UUCP (Bennett Broder)
Organization: The Broder Residence, Holmdel, NJ  07733
Lines: 30
Keywords: CD CD-ROM Audio Data

In article <1787@jade.BERKELEY.EDU> kbwalker@violet.berkeley.edu(Kevin Baranski-Walker) writes:
>What would it take to hack an audio CD to function as a CD-ROM?
>
>All of the literature that I have found hint that this may be possible but
>stop short of the particulars.  Would a three laser drive be neccessary in lieu
>of a single laser (or preferred)?  Many of the CD's are signifigantly in-
>expensive that even with the addition of an SBC the total cost would still
>be much less than the commercial CD-ROM drives available.

I am not familiar with CD ROM drives, but I can tell you that there is
no such thing as a three laser audio CD player.  What you are probably
thinking of is a 'three beam' player.  In a three beam player the laser
light is split into three beams using a diffraction grating.  The main beam
is used to read the data, while the two auxiliary beams are aimed half on-
half off the pits of the adjacent tracks.  Two photodetectors compare the
light from the aux beams; when one gets darker than the other, the player
knows that the pickup has drifted and makes an appropriate correction.

Single beam units have to derive the same information by looking at the
at the reflected light from the main beam.

I expect that the three beam method would probably be prefered for
CD ROMS, since it seems to be more forgiving of damaged disks (particularly
eccentric disks) in audio applications.

-- 

Ben Broder
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