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Self-Defining Disk Directory With Common Accessing Algorithm

IP.com Disclosure Number: IPCOM000102577D
Original Publication Date: 1990-Dec-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 4 page(s) / 143K

Publishing Venue

IBM

Related People

Batalden, GD: AUTHOR [+4]

Abstract

A "self-defining" directory for a removable media is described. That is, the directory information is treated like any other file, and the "directory file" is, in turn, recorded as just another file within the directory. This technique then allows the handling of the directory with code developed to handle ordinary files. Further, the directory can now be located at an arbitrary location on the media. This gives the system the flexibility to locate the directory in a location advantageous to a particular use or function. And, finally, the size of the directory can be modified dynamically. The directory can be expanded or made smaller as required.

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Self-Defining Disk Directory With Common Accessing Algorithm

       A "self-defining" directory for a removable media is
described.  That is, the directory information is treated like any
other file, and the "directory file" is, in turn, recorded as just
another file within the directory.  This technique then allows the
handling of the directory with code developed to handle ordinary
files.  Further, the directory can now be located at an arbitrary
location on the media.  This gives the system the flexibility to
locate the directory in a location advantageous to a particular use
or function.  And, finally, the size of the directory can be modified
dynamically.  The directory can be expanded or made smaller as
required.

      The technique described allows the disk directory to be treated
like any other file.  An advantage of this approach is that the
normal file operations, such as extension or truncation, are now
easily done on the directory.  Another advantage is that the
directory is handled with the normal file manipulation code.  This
eliminates the special code needed only to handle the directory.

      The technique sets some conditions on the use of the media
space.  The biggest constraint is that all space on the media is
located in some file.  Free space, directory space, user space, it
makes no difference.  All space resides in one, and only one, file.
There are two major reasons for this:  simplicity and accountability.
Briefly, for simplicity, one piece of file handling code is allowed
to handle any file - user, directory, or free space.  For
accountability, it is easy to quickly verify the directory integrity
if every space on the media should be in one, and only one, file.

      However, not everything can be floating free at any location on
the media.  While the use of some unique identifiers might make it
possible to locate some key items of information, it is much simpler
and less prone to error if something is at a definite location.  This
directory structure utilizes the first 128 logical blocks of the
media for "special" purposes.  In logical block 6, there is
essentially a description of the directory.  This includes the
starting location and size.  However, one goal was to avoid being in
a failure situation if a particular sector or block was bad.  To
avoid this, the first 128 blocks are duplicated in the following 128
blocks.  Therefore, operations can proceed normally if either block 6
or its duplicate is available.  If both blocks are lost, it is still
possible to scan for the directory file location. Continued

      This "special" utilization of the first 256 blocks of the media
introduces the "reserved" file.  This "reserved" file is an ordinary
file with an entry in the directory. When the media is initialized,
this file is created and it consists of the first 256 blocks on the
media.  While no "normal" file operations will be performed with this
file, it is logica...