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Layered Removable Media Directory Definition

IP.com Disclosure Number: IPCOM000102570D
Original Publication Date: 1990-Dec-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 3 page(s) / 148K

Publishing Venue

IBM

Related People

Gregg, LE: AUTHOR [+3]

Abstract

Described is a directory system designed for use with large removable media. The assumption is that interchange between systems and applications will be common. To facilitate this, the directory structure is layered, and each layer imposes only the structure required by the operations done at that layer. This method permits basic structures, such as allocation mechanisms, to be implemented only once, while permitting emulation of any existing or proposed file system. Further, by providing a formal way of registering (and, therefore, distinguishing) each file system, only the incremental investment of the specific custom details of that file system need be made. How to place an entry in the directory, how to allocate space on the file, and many other key parts of a file system need only be written once.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 43% of the total text.

Layered Removable Media Directory Definition

       Described is a directory system designed for use with
large removable media.  The assumption is that interchange between
systems and applications will be common.  To facilitate this, the
directory structure is layered, and each layer imposes only the
structure required by the operations done at that layer.  This method
permits basic structures, such as allocation mechanisms, to be
implemented only once, while permitting emulation of any existing or
proposed file system.  Further, by providing a formal way of
registering (and, therefore, distinguishing) each file system, only
the incremental investment of the specific custom details of that
file system need be made.  How to place an entry in the directory,
how to allocate space on the file, and many other key parts of a file
system need only be written once.

      The basic premise of this directory structure is that some
basic information is required to manage the media. This information
includes things like file names, sizes, and locations.  However,
operating systems and applications require more information for their
operation.  Further, different operating systems may "require"
different data.

      To accommodate both the media management and an operating
system and applications, the data recorded in the media directory is
divided into 3 distinct parts:
      -  the rules for naming a file,
      -  the data required for media management, and
      -  data wanted by an operating system or application

      DEFINING AND REGISTERING THE OVERALL MEDIA DIRECTORY The
overall allocation mechanisms, what a directory entry generically
looks like, and how to locate it, are definable in a "universal"
manner.  This is done by having the "name" of the file be a large,
but fixed number, and to provide definitions of "alias" files,
subdirectory files, and then establishing rules for allocating space
on the media using extents.  Finally, as will be shortly described,
you need to describe the file's directory entry itself. Allocation is
not further described; any of the common means can be used as long as
it is well-defined; it can be completely common and standard.
Likewise, the layout of the directory and its names is not further
described.  Any reasonable method can be used as long as it supports
the above notions.

      While the above is universal, not all systems can cope with
what amounts to the "union" of all common directory structures.
Therefore, there will be a "volume table of contents" or equivalent
structure which has some form of declaration of which options are
enabled.  Each variant chosen would define its custom rules for the
above variations (whether subdirectories exist, for instance, and any
restrictions on the file name character set).

      By having a number at a fixed VTOC offset, it is possible to
know which set of rules is in use.  Systems which provide native
acces...