Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!ames!amdahl!oliveb!cygnet!mark
From: mark@cygnet.CYGNETSYSTEMS (Mark Quattrocchi)
Newsgroups: comp.ivideodisc
Subject: Re: CD-ROM
Message-ID: <686@cygnet.CYGNETSYSTEMS>
Date: 14 Jan 88 21:27:25 GMT
References: <19898@teknowledge-vaxc.ARPA> <4469@watdragon.waterloo.edu>
Reply-To: mark@cygnet.UUCP (Mark Quattrocchi)
Organization: Cygnet Systems -- Sunnyvale, CA
Lines: 34

In article <4469@watdragon.waterloo.edu> daford@watdragon.waterloo.edu (Daniel Ford) writes:
>In article <19898@teknowledge-vaxc.ARPA> rburns@teknowledge-vaxc.ARPA (Mr. Doom and Gloom) writes:
>>1) Is it possible to write to both sides of a CD? If some wished to
>>create a double sided CD which the user would switch like a phonograph 
>>record, would this be feasible?
>
>As I understand it, CD ROM discs in their current form could not be
>double sided.  I don't have my reference books with me a the moment,
>but I believe the thickness and refractive index of the plastic
>covering the pits is crucial to the accurate focusing of the laser or
>lasers (some drives have more than one) on to the track.  Basically,
>if this is true, would need a disc twice as thick. 
>
>Another simple problem with two sided discs is labeling.  Where would
>you put the name of the disc?  LP's get around this problem by being large,
>not really a solution here....
>
>>2) Has anyone announced development of a WORM media which is compatible
>>with CD-ROM readers? I have the feeling there really isn't anything
>>highly practical yet for small volume CD production. I know I would find
>>such a system HIGHLY attractive, even if it lacked some of the
>>performance of existing WORM media.
>
>I believe that it may be possible to construct a drive that would read
>both CD ROM and WORM discs but there are some problems.  The big one is
>the different recording formats used in the two types of disks.  
>CD ROM is CLV (constant linear velocity) and WORM is CAV (constant angular
>velocity).  A CD ROM drive varies the speed of rotation of the disc
>while a WORM drive does not.  It would be tricky but not impossible, 
>maybe somebody out there knows more about such a beast...

Not true. All of the 5 1/4" worm drives are currently using the CLV
format in order to increase the density up to about 600 meg per disc
(double sided). The 12" market is also working on the CLV format which
would give them a total capacity of about 4 gigabytes per platter.