Interface protocols
  The low level protocols of bit/byte definition have been defined.
    And audio is a standard protocol.

  However, protocols for 'data' access (filenames, directories, permission) 
    are also required by computers and their operating systems.

  Macs, Win-tel, Linux, Unix

  Early on, the computer industry insisted on a single standard that 
    was compatible on different systems.

  Known originally as High Sierra, it evolved into ISO 9660.
    circa 1986/1988

  Primarily used for CDs, but can be used for DVDs, and Blue-Ray discs,
    with some limitations.

  ISO 9660 has three levels defined - new standard coming.
    Wikipedia : ISO 9660

Data format (computer data) - ISO 9660
  ISO 9660 attempts to be flexible enough for use by different OSes.
    Upper case letters, numbers, underscore.
    No spaces.
    Filename cannot start or end with period.
    Only 1 period in a name.
    Directory name cannot contain period.

  Level 1
    8 character file name with a 3 character extension.

   Directories can be eight deep.
     Directory names may not use the 3 character extension.

     All files must be recorded contiguously (sequentially in single write).

  Level 2 - 32 character filenames (or possibly more)

     Directory/filename may be up to 180 characters depending on presence of
       extended file attributes 
       * filename area holds additional file attributes.

  Level 3 - Non-contiguous writes (for re-writable disks).

    Mac OSX cannot handle level 3 (?) but can read Rock-Ridge extensions.

  ISO 9660 uses extents to provide flexibility to its design but the OS
    accessing it must recognize them. (Rock Ridge, El Torito, Joliet, etc)

  ISO 9660 allows maximum of 4 GiB of storage with some older OSes only 
    recognize 2 GiB because of use of signed counters.
 
    A technique of using extents to chain sectors can get around the 4 GiB 
      limit but may not be readable by different OSes.
    
  * Many Data DVDs use the ISO 9660 protocol.
 
  Extension :
    Joliet - add Unicode support.
    Rock Ridge - Posix (Unix) attributes.
    ISO 9660:1999 - longer filename paths and directory structure > 8 deep.
    El Torito - provides boot-able CDs. 1994/5
    Apple ISO 9660 - Mac OS specific features.

  Rock Ridge - Unix specific protocol that supports Unix i-node file-system.
    reference to Blazing Saddles.
    
    Filenames - 255 bytes.
    Larger variety of non-alphanumeric characters.
    Unix-type file modes and user and group ids.
    Symbolic link support.
    Deeper sub-directory support.    

  Macintosh uses its own standard  HPFS (built on top of ISO 9660?)
    This is why commercial CDs are careful to indicate compatibility.
      Or use a "neutral" protocol.

  Newest : UDF - universal disc format which supports packet writing and
    the ability for an OS to treat the CD-r as a big floppy. 
  
    More common on DVDs.

    Several versions, 1.02, 1.50, 2.0x, 2.50, 2.60, VAT, Sparing tables.
    Different OSes will support different extensions or some aspect of them.
      May require use of 3rd party software.
 
    * Sparing - r/w disc (re-writable) do fatigue. Sparing distributes the
      modifications so all sector get evenly used. 

    Wikipedia Universal Disk Format