The various logical structure of a directory is as follows:
§ Single Level Directory
§ Two Level Directory
§ Tree Structure Directory
Single Level Directory:
§ It is the simplest form of directory structure having only one level of directories.
§ All the file are contained in the same directory.
§ So, all files should have unique name that no two users can have same file name as the files of all users are stored in same directory.
§ It is simple, easy to understand.
§ Easy to find the file.
§ It requires unique file names so no two users can have a same file name.
§ It does not provide the method to organise the files.
§ It is difficult to remember all file names and creates files with unique name.
Two Level Directories:
§ This kind of directory structure supports two levels of directories that a Master File Directory and User File Directory as sub- directories of master directory.
§ In This Structure, Different users have different directories containing their own files only.
§ In this system, the combination of user name and file name serves as pathname for a file. When a user refers to a particular file, his own User File Directory is searched.
§ The file of different users is separated from each other as each user has its own directory.
§ It solves the problem of name-collision as observed in single level directory. Two users can have same file name in their own directories.
§ Search options for files are efficient as compared to single level directory structure.
§ Sharing of file by different users is difficult.
§ Some systems do not allow sharing the files.
Tree Level Directory:
§ It is the most common, powerful and flexible structure implemented in almost every operating system.
§ It is just extension of two level directory structures.
§ It uses the same concept of two level directory structure of master file directory having user file directories as subdirectories.
§ Each user has User file Directory and sub directories and files.
§ In tree structure, file can be referred in two ways: Absolute Pathname andRelative Pathname
§ Absolute Pathname starts from the root directory and ends at the required file following a path of directories and subdirectories. For example: the path c:/windows/pro/abc.txt represents the absolute path.
§ Relative Pathname starts from the current directory to the file. For example: /user/cd. then a file whose absolute path is /user/cd/ss can be referred simply as ‘ss’.
§ It is simple and easy to use. All users have different directories and their subdirectories.
§ Now different users can keep the same file name in their own directories.
§ It provides efficient searching by absolute or relative path.
§ The files cannot be shared of different users.