Conference cookie::notes$archive:cd_v1

432.0. "<< CD Technology >>" by RDGE28::LINTON (Peter Linton, ADG UK) Wed Aug 20 1986 10:35

	Me again. [8v)-

	Just read a short piece on CD-ROMS in a mag and thought I
	would pass on the info. to you. I expect there is a note on
	the underlying technology of CD's in this file, but that may
	well have been a long time ago.

	PRACTICAL COMPUTING, SEPTEMBER 1986

        A CD-ROM disc holds information in pits that are burned into its
	surface. There is room for about 2 billion pits on a single disc.
	During the mastering process the pits are burnt into the surface
	of the master disc by laser beam. The lens controlling the laser
	beam moves radially while the disc spins, so the information is
	laid down in a spiral track.

	The surface profile of the master is then copied either by electro-
	plating or by photopolymer replication onto physical negatives. The
	CD-ROM discs themselves are mades out of a transparent polycarbonate
	plastic, and are usually formed from the negative by an injection-
	moulding process. The surface is the coated with a reflective layer
	of metal, usually aluminium, followed by a protective layer of
	lacquer.

	Most CD-ROM players use a small Gallium Arsenide semiconductor laser
	to generate the light beam which reads the information from the disc.
	Light striking the pits if diffracted, while light that strikes the
	area in between is reflected. A photo-detector collects the reflected
        light and generates a modulated signal corresponding to the pattern of
	the data recorded on the disc.

	This signal is the decoded and converted to digital data suitable for
	use by a computer.

                                    ENDS.

	The principle would be the same for audio-CD's except for the last
	sentence I suppose ??


	BFN  Peter Linton. 

    There is actually a CDROM notes file for discussing this sort
    of thing.  DEC is into it in a big way.
    
    I just saw a copy of the VMS source listings on CD.  It comes in
    a jewel box just like your home CDs.  I hear it sounds terrible,
    though (even though it's DDD :-)
    

    re .1: 
    
    Someone should look into selling a few of those VMS source
    listing CD's to Newbury Comics :-).  Even at our asking price
    ($400.00?) they'd probably sell out.  There's stranger (well, almost)
    stuff in those bins at Newbury!
    
    

I've played VMS.  It was after a day of hacking on my Pro-350 here at home,
and VMS was certainly music to my ears...

Sorry, couldn't resist.  It actually sounds quite a bit like spitting the
taskbuilder out my Pro-350 TMS.

/john

    Sick.
    
    - M

    PYRITE's network database is dated April 29??????????????????????????
    
    - M