🚀 go-pugleaf

TAMIL@QUCDN.QueensU.CA) wrote:

> OK, I was thinking about this for couple of days now, since CD-ROM, and
> video disk uses about the same kind of procedure to read data
> why cant we make the video disk to read digital data we cab store
> all the info in digital format rather then analog, by my calulation a
> video disk can hold about 6.5 GByte of Data.

LDs don't use the same kind of procedure.  The laser frequency is the same,
and the pits are 1/4-wave reflective, but the LD signal is pulse-FM analog
(at about 9MHz) rather than the raw 1.5MHz binary stream of CD.  LD is
analog video, analog audio, and optionally digital audio.  The digital audio
is a binary stream added to the pulse-FM carrier at -26dB, essentially
becoming a duty-cyle modulation of the FM.

If RedBook (CD) format was used on LD, the capacity would be impressive.  As
it is, an "LD-ROM" (using the digital audio channel for data) only stores
600 Mbytes (or less) per CLV side, since LDs are 60 minutes per side, 
compared to CDs at 72 min/side.

Regards,                                              Hewlett-Packard
Bob Niland      Internet: rjn@FC.HP.COM               3404 East Harmony Road
                CompuServe:  71044,2124               Ft Collins CO 80525-9599

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