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cdrom(4)							      cdrom(4)

       cdrom - CD-ROM background information

       This manpage provides general information on existing CD-ROM standards,
       terminology, data layout, and levels of support.	 More detailed	infor‐
       mation is available in the standard documents listed in

       Not  all	 topics	 discussed  here  are  supported  in the current HP-UX
       release.	 Refer to the section for details about the  contents  of  the
       current release.

   Standard Formats
       Currently, two standard formats are defined for CD-ROM.

       The  High Sierra Group (HSG) standard was produced by the CD-ROM Ad Hoc
       Advisory Committee, and is documented in a  publication	entitled  This
       document is available from the National Information Standards Organiza‐
       tion (NISO).

       The second standard, which evolved from the HSG standard, was  produced
       by  the	International  Organization  for  Standardization (ISO).  This
       standard is documented in a publication entitled reference  number  ISO
       9660: 1988 (E).

   Data Layout
       The data layout on a CD-ROM can be represented as follows:

			   │ System Area - 32 kilobytes	  │
			   │	  Volume Descriptor	  │
			   │		  .		  │
			   │		  .		  │
			   │		  .		  │
			   │ Volume Descriptor Terminator │
			   │		  .		  │
			   │		  .		  │
			   │		  .		  │
			   │	     Path Table		  │
			   │	     Path Table		  │
			   │		  .		  │
			   │		  .		  │
			   │		  .		  │
			   │   Directory and File Data	  │
			   │		  .		  │
			   │		  .		  │
			   │		  .		  │
       There are typically four─sections─in─the─CD-ROM─data (indicated by dou‐
       ble horizontal lines in the table above): Only the first	 two  sections
       must occur in the order shown above.

       The  consists  of the first sixteen 2048-byte blocks on the media.  The
       contents of this section are not specified by  either  standard;	 here,
       the  creator  of the CD-ROM can put data that is relevant to the system
       for which the CD-ROM is intended.

       The typically contains one primary volume descriptor and zero  or  more
       supplementary volume descriptors.  Each volume descriptor is 2048 bytes
       in length, and describes the attributes and structure  of  a  directory
       hierarchy  on the CD-ROM.  The list of volume descriptors is terminated
       by one or more A volume descriptor terminator is	 also  2048  bytes  in
       length, and simply signals the end of the volume descriptor section.

       The  contains  all the path tables for all directory hierarchies on the
       CD-ROM.	Path tables do not have to be constrained to this  section  of
       the CD-ROM data, but can be interspersed with (described below) to min‐
       imize seek times.

       The contains data for all directory hierarchies on the CD-ROM  and,  as
       described  above, can be made noncontiguous by the occasional inclusion
       of a path table.

   Volumes and Directory Hierarchies
       A is a single physical CD-ROM.  A is a hierarchical file system written
       on  a volume.  Multiple directory hierarchies can be placed on a single
       volume, or a single directory  hierarchy	 can  span  multiple  volumes.
       Each directory hierarchy on a volume is described by a

       Directory  hierarchies on the same volume can be totally independent of
       each other with each one defining a totally unique and  unrelated  file
       system.	 They can also be related to each other through the sharing of
       data between them.

       A is a set of one or more volumes that are to be	 treated  as  a	 unit.
       Each  successive	 volume in the volume set updates or augments the data
       on the volumes preceding it.  Thus, the last volume in a volume set  is
       always the volume which describes the most up-to-date directory hierar‐
       chy for the volume set.	A unique and ascending	value  called  the  is
       assigned	 to  each  volume in a volume set.  Volume sets are useful for
       updating large multivolume  databases  without  having  to  rework  the
       entire set.

   Volume Descriptors
       Each  directory	hierarchy on a volume is described by a There are sev‐
       eral types of volume descriptors, but the two of most interest are  the
       and  the	 Their	content	 is  almost identical, but they have different
       intended uses.

       The primary volume descriptor describes the primary directory hierarchy
       on a volume.  If there are additional directory hierarchies on the vol‐
       ume, or different ways to view the same directory hierarchy, these  are
       described by supplementary volume descriptors.  In the case of a volume
       set, the primary volume descriptor on each volume describes the primary
       directory  hierarchy  for  that volume and all preceding volumes in the
       set thus far.

       Volume descriptors contain the following information:

	      standard ID (identifies the format of the volume);
	      system ID;
	      volume ID;
	      size of the volume;
	      volume set size;
	      volume sequence number;
	      logical block size;
	      path table size;
	      pointers to the path tables;
	      directory record for the root directory;
	      volume set ID;
	      publisher ID;
	      data preparer ID;
	      application ID;
	      copyright file name;
	      abstract file name;
	      bibliographic file name (ISO only);
	      volume creation date and time;
	      volume modification date and time;
	      volume expiration date and time;
	      volume effective date and time;
	      application use area.

   Path Tables
       A defines a directory hierarchy structure within a volume.   Each  path
       table  contains	a record for each directory in the hierarchy.  In each
       record are kept the  directory's	 name,	the  length  of	 any  extended
       attribute  record associated with the directory, the logical block num‐
       ber of the block in which the directory begins, and the number  of  the
       parent  directory for that directory.  (All directories in a path table
       are numbered according to the order in which they appear	 in  the  path

       There  are  two types of path tables.  One is a path table in which all
       numerical values in each path table record are recorded	least-signifi‐
       cant-byte-first.	  The other type, is a path table in which all numeri‐
       cal values are recorded most-significant-byte-first.  One of each  type
       of  path	 table is required by both standards.  The ISO standard allows
       for one additional optional copy of each type of path table, while  the
       HSG  standard allows for up to three additional optional copies of each
       type.  Additional copies of path tables are useful  for	redundancy  or
       seek time minimization.

   Extended Attribute Records
       An (abbreviated ) is a data structure specifying additional information
       about the file or directory with which the XAR is associated.   An  XAR
       contains the following information:

	      owner id;
	      group id;
	      creation date and time;
	      modification date and time;
	      expiration date and time;
	      effective date and time;
	      record information;
	      application use area.

       If  an XAR is recorded, the XAR is written beginning at the first block
       of the file or directory.  The actual data for the file or directory is
       written	beginning  at  the next block after the block in which the XAR

       Where possible, XAR information is mapped into the  stat	 structure  by
       the  system  call  (see	stat(2)).  However, many items do not map very
       well due to lack of appropriate fields in the stat structure for infor‐
       mation  provided by the XAR.  To preserve backward compatibility of the
       stat structure, such information is discarded by The system call can be
       used  to	 obtain	 the  XAR  for	a  particular  file  or directory (see

       For performance reasons,	 data  in  a  file  can	 be  interleaved  when
       recorded on the volume.	This is accomplished by dividing the file into
       pieces called The size of each file unit (in logical blocks) is	called
       the  The interleaved file is then recorded onto the volume by writing a
       file unit, skipping one or more	blocks,	 writing  another  file	 unit,
       skipping more blocks, and so on until the entire file is recorded.  The
       number of blocks to skip between file units is called the Blocks making
       up the interleave gap are available for assignment to other files.

       File unit and interleave gap sizes are kept in the directory record for
       each file.  Thus, the file unit and interleave  gap  sizes  may	change
       from  file  to file, but cannot change within the same file (unless the
       file is written in − see below).

       Directories cannot be interleaved.

   File Sections
       In order to be able to share data between files, a file can  be	broken
       up into File sections for a particular file are not necessarily all the
       same size.

       Each file section is treated like a separate file in that each  section
       gets its own directory record.  This implies that each file section has
       its own size, its own XAR, and its own unique file unit and  interleave
       gap sizes.  However, all file sections for the same file must all share
       the same file name.  The order of the file  sections  in	 the  file  is
       determined  by  the order of the directory records for each section.  A
       bit in each directory record determines whether or not that  record  is
       the last record for the file.

       A  file	section	 can appear more than once in a single file, or appear
       many times in many different files.  A file section in one  volume  can
       also  be claimed by a file in a subsequent volume in a volume set (this
       is how updates are accomplished).

       Each file section can have its own XAR.	However,  if  the  final  file
       section	of a file has no associated XAR, the entire file is treated as
       if it has no XAR.  This is done to make updates work sensibly.

       Directories must always consist of a single section.

   Implementation and Interchange Levels
       CD-ROM standards define two levels of implementation and	 three	levels
       of  interchange.	  provide a way for receiving systems that support CD-
       ROM to specify their level of support.  The implementation levels are:

	      Level 1	  The system is permitted to ignore supplementary vol‐
			  ume  descriptors,  their associated path tables, and
			  all directory and file data associated with them.

	      Level 2	  No restrictions apply.

       In all cases, receiving	systems	 must  fulfill	the  receiving	system
       requirements specified in section 10 of the ISO standard (no equivalent
       section exists for HSG).

       provide a way to specify the data structure and complexity that	exists
       on a CD-ROM.
	The levels are:

	      Level 1	  Each	file  consists of a single file section.  File
			  names contain no more	 than  eight  characters,  and
			  file	name  extensions  contain  no more than three.
			  Directory names contain no more than	eight  charac‐

	      Level 2	  Each file consists of a single file section.

	      Level 3	  No restrictions apply.

       HP-UX  supports	only  the primary volume descriptor.  When a volume is
       mounted, HP-UX mounts the directory hierarchy described	by  the	 first
       primary	volume	descriptor it finds.  Supplementary volume descriptors
       are recognized and ignored, as are their associated  directory  hierar‐

       Directory hierarchies spanning multiple volumes are not supported.

       Volume sets consisting of more than one volume are not supported.

       Path  tables  are ignored in HP-UX.  The normal path name lookup scheme
       used in HFS file systems is used instead.  This is done to allow	 other
       mountable file systems to be mounted on top of a mounted CDFS file sys‐
       tem.  Also, since HP-UX maintains a cache of  cdnodes  for  CDFS	 files
       (see  cdnode(4)),  the  additional  performance	gains provided by path
       tables are minimal.

       HP-UX does not support multiple	file  sections.	  Each	file  must  be
       recorded in a single file section.

       HP-UX supports level 1 implementation and level 2 interchange.

       fsctl(2), stat(2), cdnode(4).

       Ref. No. ISO 9660: 1988 (E).

       National Information Standards Organization [Z39].


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