Conference cookie::notes$archive:cd_v1

    The stream of data begins at the center, and spirals outward.  In fact,
    the rotational velocity decreases from about 500 rpm at the inside end
    to about 200 rpm at the outside to maintain constant linear data
    density.  I think those numbers are correct, but I'm not entirely sure. 

I also heard some tale that the 4 and 1/4 inch size (rather
that 4 inch) was due to the chairman of Sony wanting his
favorite edition of Bethoven's 9th to fit onto one disk.

Has anyone else heard this?

    The specific number I heard was that the capacity in minutes
    of a compact disk had to be sufficient to accommodate Beethoven's
    Ninth, or about 70 minutes.

    re:.4 re:.3
    
    That's what I've heard, the specific figure being 74 minutes.
    
    As I mentioned in the "Hall of Fame" note, one presumes that the
    longest CD is some version of the Ninth.
    
    --- jerry

As I understand it the basic reasoning for starting the music at the
inside was twofold:

1) When they started initial develpment of the mechanics they had not
   settled on final dimensioning so starting the music at the inside
   was a good bet since they basically knew there would be an inside -
   they did not know where the outside would end up.

2) Secondly, the inside area of the disk is less prone to being screwed
   up in handling/manufacture etc. so if any space were to be left blank
   better it be on the edges where all our fat fingers go.

-peter

    Re: Magnetic Disc drive positioning
    
    The reason magnetic fixed disc drives automatically position to
    the inner tracks (RD52, RD53) and recommendations for positioning
    others to the inner tracks (RD50, RD51, RD31) is that there is a
    nice chunk of media at the inner radius that cannot reliably contain
    customer data due to head/media physics. This is an ideal place
    to 'land' the heads as a result. 
    
    Shock and vibration characteristics do not change, its just that
    it is less likely to affect customer data if head slap or other
    problems occur while the drive is shut down.
    
    Walt 

    An interesting advantage to the data beginning at the center is
    that it opens the possibility of manufacturing smaller discs that
    are compatible with today's players.  Since the discs all start
    in the same place, a smaller disc should play ok.  Will we soon
    see CD singles?
    
    -Rick

    Well, I know of at least *one* CD single (though one might call
    it an EP) --- Suzanne Vega's LEFT OF CENTER. It has three songs
    (two of them from her first album, and the title number from the
    PRETTY IN PINK soundtrack) and the total time is just a hair
    under ten minutes.
    
    --- jerry

    re .9
    I hope you weren't charged $14 for your ten-minute CD "single",
    Jerry?  And where did you find it?

    Several years after 12" LV had been on the market, Pioneer began
    releasing 8" cheapies (about � price).  Although their advertising
    seemed to indicate that the smaller discs would only play on the
    newer LV players, the generation 1 players handled them fine.
    
    -- Ward

        I hope "they" don't start making "45"-ish CDs until they
        have enough factories, etc., to (more than) keep up with
        the demand for album-length CDs.
        
Jim Stratton
        

Apart from considerations mentioned so far, the question of where to
start track one is a purely technical one.

LPs, being CAV, provide the best performance at the outer edge.
Since most LPs are shorter than their maximum possible time (sigh),
it made good sense to start at the outer edge. 

CDs, on the other hand, are CLV, so the above consideration no
longer applies. It can be shown, however, that read error density is
much higher at the outside diameter. Since most CDs are shorter then
their maximum possible time (sigh...), it made sense to start at the
center. 

-- Ron 

CAV = Constant Angular Velocity
CLV = Constant Linear Velocity

    re: .-1 and .-2
    
    These are LaserDisc terms (at least, that's how we see them most
    often).  In a CAV disc, the disc rotates at a constant speed throughout
    the playing (Constant Angular Velocity); thus, the data near the
    center is "more compressed" than that at the edges.  In a CLV disc,
    the speed of the disc changes as the laser moves outward from the
    center (but since the disc also gets bigger, the laser covers the
    same distance; Constant Linear Velocity).
    
    CDs are CLV, and LaserDiscs come in both types.
    
    					Vernon
    
    

    Re: .-1
    
    Change the phrase "speed of the disc changes" to read "speed of
    the disc decreases".  I failed to indicate HOW it changes!!