As shown in figure 1421 in this method the disk

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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 directory structure. 3. 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.

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