Technical data

Managing Storage Media
Concept Section
Tape and disk volume protection Section 9.4
Disk volume sets Section 9.6.1
Disk quotas Section 9.11.1
Mount verification Section 9.13.1
9.1 Understanding Storage Media Concepts
The following list contains concepts related to storage media in general:
Term Definition
Device (or Drive) Hardware that allows access to storage media.
Media Physical items on which you can store data.
Volume Logical unit of data storage; one or more media units. A disk or
tape must be mounted on a device for the operating system to
recognize itas a volume.
The following sections use these terms to explain media concepts.
9.1.1 Disk and CD–ROM Concepts
This section defines terms related to disks and CD–ROMs. It also compares
on-disk file structures and explains the ISO 9660 standard.
9.1.1.1 Disk Terminology
Disks are physical media on which files reside. On–Disk Structure (ODS) refers
to a logical structure given to information stored on a disk; it is a hierarchical
organization of files, their data, and the directories needed to gain access to them.
The OpenVMS file system implements the ODS and provides access control to the
files located on the disk.
Compact disc read-only memory (CD–ROM) discs and readers used with
computers are very similar to the CD–ROMs used for audio applications. The
major differences are that CD–ROM drives have a digital (rather than an audio)
interface, and that CD–ROM discs employ additional layers of error correction
and formatting to encode data blocks.
The advantages of storing data on CD–ROMs rather than on tape or other
removable media are:
• You can access data directly, which you cannot do with tape.
• CD–ROMs are much less expensive than other direct-access media. They are
typically used for publishing and distribution.
• CD–ROMs have exceptional storage space capability. A CD–ROM can hold
approximately 650 megabytes of data.
Table 9–1 defines terms as they apply to disks and CD–ROMs.
9–2 Managing Storage Media