Disc Areas

Recording order on the disc (Track Structure)

===============================================



Legend:

  I     Lead-in area (leader space near edge of disc)

  D     Data area     (contains actual data)

  O     Lead-out area (leader space near edge of disc)

  X     un-usable area (edge or donut hole)

  M     Middle area (interlayer lead-in/out)

  B     Dummy bonded layer (to make disc 1.2 mm thick instead of 0.6mm)



Single layer disc:

  direction: continuous spiral from inside to outside of disc.



       |   ----------------------->

       |BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB     outer edge 

       |XXIIIDDDDDDDDDDDDDDDDDDDDDOOOXX     of disc

       |



      reference

      axis



Dual layer disc:



  (A) Parallel track path (for computer CD-ROM use)

    Direction: same for both layers.                     

    

          ----------------------->

        XXIIIDDDDDDDDDDDDDDDDDDDDDOOOXX    Layer 1

        XXIIIDDDDDDDDDDDDDDDDDDDDDOOOXX    Layer 0

          ----------------------->

                         



  (B) Opposite track path (for movies)

    Direction: opposite directions 

     Since the reference beam and angular velocities are the same

     at the layer transition point, the delay comes from refocusing.  

     This permits seamless transition for movie playback.

    

          <----------------------

      XXOOOODDDDDDDDDDDDDDDDDDDDDMMMXX    Layer 1

      XXIIDDDDDDDDDDDDDDDDDDDDDDDMMMXX    Layer 0

          ----------------------->