Directory Structure Single Level Directory Two Level Directory Tree Structured Directories Acyclic Graph Directories General Graph Directories

Directory organization Device or File System Directory the structure and the organization of keeping the files and catalogs on the storage. On 1 disk there are 2 partitions each one has a device directory. One partition contains 2 disks and has 1 device directory.

Directory operations The system directory can be viewed as a symbol table that translates file names into their directory entries. If we take such a view, we see that the directory itself can be organized in many ways. We want to be able: to insert entries to delete entries to search for a named entry to list all the entries in the directory. File Read and File Write – are these directory operations or not?

Tricky permissions Who can Write or Read the .bashrc file? To Delete the .bashrc file means to make changes in /home/studnt directory list To see who can make changes in this directory we look into upper directory list’s record. Who is able to delete studnt directory from the home catalog ? Who can Write or Read the .bashrc file? Who can delete the .bashrc file?

Single Level Directory

Two Level Directory Disadvantages: The idea of path name search path Advantages: File Names should be unique only in UFD. Each User sees only his UFD. Their spaces are isolated. Disadvantages: No possibility to create subdirectories for further grouping files Problems: Sharing of files between users should be somehow organized. If the files are shared then the username:filename pair (path) uniquely defines the file for each user even if they have the same filename.

Tree Structured Directories Create as many directories as you want group the directories and files as you want. However there is no sharing.

Acyclic Graph Directories

Acyclic graph example

Acyclic graph example

Acyclic Graph Problems

General Graph Directories when we add links to an existing tree-structured directory, the tree structure is destroyed, resulting in a acyclic graph structure. when we add cyclic links to an acyclic graph structure we get general graph structure

Cyclic links in Unix

Cyclic links in Windows Unix - Tree Structured Directory (improved to acyclic graph) Windows - 95,95, NT, 2000,… - an extended two-level directory structure, with devices and partitions assigned a drive letter. Partitions have a general graph directory structure associated with the drive letter.

General Graph Directories Garbage (cyclic self reference) collection involves traversing the entire file system, marking everything that can be accessed. Then, a second pass collects everything that is not marked onto a list of free space.