Path: utzoo!utgpu!attcan!uunet!seismo!sundc!pitstop!sun!hanami!landman
From: landman%hanami@Sun.COM (Howard A. Landman)
Newsgroups: comp.sys.next
Subject: Re: NeXT press release (very long but interesting)
Message-ID: <74011@sun.uucp>
Date: 21 Oct 88 17:50:44 GMT
References: <5423@juniper.uucp> <72886@sun.uucp> <635@ardent.UUCP> <73226@sun.uucp> <169@gloom.UUCP>
Sender: news@sun.uucp
Reply-To: landman@sun.UUCP (Howard A. Landman)
Organization: Sun Microsystems, Mountain View
Lines: 21

In article <169@gloom.UUCP> cory@gloom.UUCP (Cory Kempf) writes:
>A data CD (at least in the standards that I have used) is formatted
>in a LONG spiral.  the spiral is broken down into several blocks,
>each of which "looks" like it is 2k.  In reality, they use some
>error correction code (ECC) that causes 8 bits to use up 14 bits 
>of space.  

The 8 to 14 bit encoding has nothing to do with the error correction.
It is used to make reading and writing easier since it limits the
space between transitions.  Thus phase-locked loops stay in sync
better (transitions not too far apart), and lasers don't have to
switch so fast when writing the CD master (transitions not too close
together).

The error correction is a CIRC (Cross Interleaved Reed-Solomon Code)
which operates on a much larger scale than 8 bits at a time.  It also
has a much lower overhead than 75%!

	Howard A. Landman
	landman@hanami.sun.com
	UUCP: sun!hanami!landman