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Unformatted text preview: Name structure
attributes containing file data
address) Figure 14.18. Typical contents of a directory. There is one entry per file.
When a new file is created, an entry for it is created in the directory, and when a
file is deleted, its corresponding entry is deleted from the directory. When an
existing file is opened for use, the operating system searches its corresponding
entry in the directory and then extracts its attributes and disk addresses, and loads
them in a table in main memory. All subsequent references to the file use this
information in main memory.
The number of directories used and the way these directories are organized varies
from one system to another. The following three types of organizations are
1. Single directory. This is the simplest organization. As shown in Figure
14.19(a), in this case, a single directory contains entries for all the files in the
system. Although this organization is simple to implement, it has significant
limitations when the number of files increases or when there are more than one
users. As the number of files increases, it becomes difficult to remember the
names of all the files in order to create new files with unique names. Similarly, in
a system having multiple users, if two users choose the same file name, the system
will not accept the file name of the user who did so later than the other user
because it violates the unique-name rule. Such conflicts and confusions make this
directory organization unsuitable for multi-user systems. Hence it is used only by
the most primitive microcomputer operating systems. This organization is
popularly known as flat directory structure.
2. One directory per user. As shown in Figure 14.19(b), in this organization,
there is a separate directory for each user. The names of all the files belonging to a
particular user are listed in his/her directory. As a file name needs to be unique
only within a directory, different users can have files with the same name. This
overcomes the limitation of file name conflicts among users...
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This document was uploaded on 04/07/2014.
- Spring '14