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In most computer systems more than one peripheral storage device is used for the storage of files. It is now necessary to discuss a number of matters pertaining to the management by UNIX of the whole set of files and file storage devices. First, some definitions:
an integrated collection of files with a hierarchical system of directories recorded on a single block oriented storage device;
a device which can store information (especially disk pack or DECtape, etc.);
a mechanism for transferring information to or from a storage device;
is only accessible if it is inserted in an access device. In this situation reference to the storage device is made via a reference to the access devce;
is acceptable as a file system volume if:
information is recorded as addressable blocks of 512 characters each, which can be independently read or written.
(Note IBM compatible magnetic tape does not satisfy this condition.);
the information recorded on the device satisfies certain consistency criteria:
block #1 is formatted as a “super block” (see below);
blocks #2 to #(n+1) (where n is recorded in the “super block”) contain an “inode” table which references all files recorded on the storage device, and does not reference any other files;
directory files recorded on the storage device reference all, and only, files on the same storage device, i.e. a file system volume constitutes a self-contained set of files, directories and “inode” table;
is mounted if the presence of the storage device in an access device has been formally recognised by the operating system.
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