Unformatted text preview: in case of single
directory organization. However, this organization is still not very satisfactory for
users with many files because it becomes difficult for a user to remember the
names of all the files created over a period of time when the number of files in the user's directory becomes large. This organization is popularly known as two-level
Multiple directories per user.
As shown in Figure 14.19(c), in this
organization also, there is a separate directory for each user. However, each user
can create and use as many sub-directories or sub-sub-directories, or sub-sub-subdirectories, and so on to group his/her files in natural ways. For example, a user
may like to group his/her files project-wise, in which case a sub-directory may be
created for each project and all files pertaining to a particular project can be listed
within the corresponding project's sub-directory. As a file name needs to be
unique only within a directory, the same user can have files with the same name in
different sub-directories. This feature provides greater flexibility to a user in
naming his/her files because the files can be grouped together in logical ways and
the user can remember the file name along with the group name to which it
belongs even when the number of files for a user becomes large. This organization
is popularly known as tree-structured hierarchical directory structure.
Disk Space Allocation Methods
Files are normally stored on disks for permanent storage. A disk normally contains
many files. Disk space allocation methods deal with how to allocate space to
multiple files on disk so as to meet the following two objectives:
1. Disk space is effectively utilized, and
2. Desired piece of information can be quickly accessed from files.
The three commonly used methods for disk space allocation are contiguous,
linked, and indexed. They are described below. However, before that, it is
important to note that operating systems divide the total disk storage space into
equal sized blocks (see Figure 14.20). The size of a b...
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This document was uploaded on 04/07/2014.
- Spring '14