Re: Bit representation on a CD

From: Rich Grise (rich_at_example.net)
Date: 11/23/04


Date: Tue, 23 Nov 2004 03:49:49 GMT

On Sun, 21 Nov 2004 21:53:01 +0100, c.j[dot]w wrote:

> Hello,
>
> This question has some connections with the other one that I recently
> posted.
>
> When data is stored on a CD, a straight-forward approach would be to
> store a 0 as a land and a 1 as a pit, or vice-versa. But the
> representation used is that a 1 is representated by a change from pit to
> land or from land to pit, and a 0 is represented by a pit or a land.
>
> My questions is: Why is it better to use the transition/not-transition
> approach? I have read an explanation, but don't understand it. It is
> quoted below this post. The whole text can be found at
> http://pauillac.inria.fr/~lang/hotlist/cdrom/Documents/tech-summary.html.
>

It's called NRZ (Non-Return to Zero) recording; maybe drawing a little
timing diagram would help you see the point - it ensures that there are
enough edges to recover the clock, and stuff like that. I put "nrz data"
in google and got this results page:
http://www.google.com/search?q=nrz+data&btnG=Google+Search

Hope This Helps!
Rich