cdrom.4 (2010 09)

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cdrom(4) cdrom(4)
and File Data (described below) to minimize seek times.
The Directory and File Data 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 volume is a single physical CD-ROM. A directory hierarchy 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 volume descriptor.
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 volume set 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 hierarchy for the volume
set. A unique and ascending value called the volume sequence number, 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 volume descriptor. There are several types of
volume descriptors, but the two of most interest are the primary volume descriptor and the supple-
mentary volume descriptor. 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 addi-
tional directory hierarchies on the volume, 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 path table 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 number 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 table.)
There are two types of path tables. One is a type-L path table in which all numerical values in each path
table record are recorded least-significant-byte-first. The other type, type-M, is a path table in which all
2 Hewlett-Packard Company − 2 − HP-UX 11i Version 3: September 2010