Path: utzoo!mnetor!uunet!husc6!rutgers!clyde!watmath!watdragon!daford
From: daford@watdragon.waterloo.edu (Daniel Ford)
Newsgroups: comp.ivideodisc
Subject: Re: CD-ROM
Message-ID: <4469@watdragon.waterloo.edu>
Date: 3 Jan 88 03:13:49 GMT
References: <19898@teknowledge-vaxc.ARPA>
Reply-To: daford@watdragon.waterloo.edu (Daniel Ford)
Organization: U. of Waterloo, Ontario
Lines: 38

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...


					Dan Ford

-- 
---------------------------------------------------------------------
Daniel A. Ford 					daford@watdragon.uucp
CS Department                         daford%watdragon@waterloo.csnet
U. of Waterloo       daford%watdragon%waterloo.csnet@csnet-relay.arpa