Conference cookie::notes$archive:cd_v1

    re:.0
    
    (1) The standard max time is 74 minutes and mumble seconds.
    	There have been a couple of CD's released that go over that
    	maximum, but the quality control is tricky the more you
    	put on. I don't know what the *real* max is, but the longest
    	CD out so far is a tad over 80 minutes.
    
    (2) From the middle out.
    
    (3) Depends on what you mean by "the shiny part". The information
    	is encoded on a layer of mylar just under the plastic coating
    	on the underside.
    
    (4) I dunno. What do you find interesting?
    
    --- jerry

	Are there any CD's that use the top, as well as the bottom?  Is
	it possible to record  on  both  sides  (if  there was no label
	printed)?

    re:.2	
    >Are there any CD's that use the top, as well as the bottom?  Is
    >	it possible to record  on  both  sides  (if  there was no label
    >	printed)?
     
    I have never seen one.  I suppose it *might* be possible, but this
    would necessitate the disc being almost twice as thick, as 95% of
    the thickness of the disc is between the pitted aluminum and the
    bottom of the disc.  This is necessary to make scratches on the
    bottom surface to be out of focus as seen from the read lens.
    
    I would expect that the quality control on a double-sided disc would
    be very difficult.  It probably would cost a lot more to make a
    double-sided disk than two single-sided ones, and the double one
    would probably work in only a few players.
    
    			Steve

    There are "double" CDs in mono.  First you play one track, then
    the other.

    A double-sided CD would violate the spec in at least 2 ways:
    
    1) The spec specifically states the media to be single sided.
    
    2) A double disc would certainly weigh significantly more than the
    specified weight of a CD, which could burn out motors, screw up speed
    stability, etc.  (If you think speed stability is easy, try playing a
    CD3 without an adapter as a flywheel in some of the old players -
    especially portables - that were made before CD3s.)
    
    B
     
    

    How many RPM's do the CD's spin at?
    
    When looking at a CD it looks like you can see where the music is
    stored, like the grooves on a record. The question is it looks like
    the same thing on both sides of the CD. What is one side one?
    

    re .6
    
    The CD's very their rotational speed from around 500 RPM at the
    beginning to around 200 RPM if the recording goes all the way to
    the outer edge.
    

    re: .6
    >   When looking at a CD it looks like you can see where the music is
    >stored, like the grooves on a record. The question is it looks like
    >the same thing on both sides of the CD. What is one side one?
     
    The aluminum used as the media to burn the pits into is so thin,
    the pits just show up on both sides.  Try holding up a CD to a strong
    light source, you can see right through it!
    
    		Steve

    Re: .8
    
    I didn't think the pits were burned into the copies.  I was under
    the impression they are made like records, the master is made, then
    the copies are "pressed"?

    re:.9
    >  I didn't think the pits were burned into the copies.  I was under
    >the impression they are made like records, the master is made, then
    >the copies are "pressed"?
     
    Oops, no, I didn't mean to imply that the copies are laser-written;
    they are indeed pressed.  But the aluminum is sufficiently thin
    that the pressing results in the pattern being visible from both
    sides of the disc.
    
    		Steve

    Another bit of info that I think most people are unaware of, is
    that the data layer (the reflective metal containing the pits) is
    actually closer the surface on the label side, thus making the data
    more vulnerable to scratches, etc. on the label side.          
    
    Ken....                                                        

    The label side is just a resin-type coating on top of the
    aluminum, and yes, it is much thinner and more prone to
    damage than the "read" side. I have a couple of CDs where
    a fingerprint ate through so that you can see it from the other
    side, which affects the playing. I also have one that has no
    coating on the label side, which no longer plays. Both were
    made by the same company (Polygram in Germany).
    
    Cross-section:
    
              ============  <- coating
              ------------  <- reflective layer
              /\/\/\/\/\/\
                            <- plexiglass with laser pits
              ------------
    
    
    Scott
    

    RE: .1 (Jerry) and .4 (Michael)
    
    The longest CD I'm aware of has close to two hours of music on it.
    Actually, I'm deducing thsi information from a review in the latest
    issue of American Record Guide. It's of a mono recording of the
    complete Wagner Ring Cycle - almost 15 hours of music on 7 CDs.
    The set comes with a little gizmo that allows you to play one track
    and then the second track on each CD. I remember seeing it on sale
    at Tower records in Boston a month or so ago.
    
    -Rich

    Re/ .13:
    
    I think the little "gizmo" that comes with this is just a switch to
    selectively turn off the left or right channel.  You could accomplish
    the same thing with a balance control on your amp or receiver.

    According to literature the CD disk has some 75 minutes of music
    and almost 600 mbytes maximum capacity. What is it for those 3"
    jobbers?

	re .14

	The little gismo is for taking the a/ left out only
	into a left right and right mono and b/ right out into 
	the same.

	Peter