Sunday, June 30, 2013
About Directory Structure
- Directory structure is referred to the way that the operating system follows for displaying the files and file system to the user in the field of computing.
- A hierarchical tree structure is used for displaying the files in a typical way.
- The special kind of string the file name uses or the unique identification of a particular file that is stored in the computer’s file system.
- Before the 32 bit operating systems actually came in to the scenario; short names of about 6 to 14 characters in size were used for the file names.
- However, the modern operating systems give permission for file names of longer length i.e., of 250 character and that too per path name element.
- The drive:\ is the root directory in the operating systems such as the OS/2, windows and DOS for example, “C:\”.
- The “\” is the directory separator but the forward slash “/” is also internally recognized by the operating system.
- A drive letter is use for naming the drives either physically or virtually.
- This also implies there does not exist a root directory that is formal.
- Rather, we have root directories in each drive that are independent of each other.
- However, one virtual drive letter can be formed by combining in to one.
- This is done by keeping a RAID setting of 0 for the hard drive.
- The file system hierarchy standard is used by the operating systems such as the UNIX and other UNIX like systems.
- This is the most common form for the directory structures used by the UNIX operating systems.
- It is under the root directory “/” that all the files and the directories are stored even if they are actually present on a number of different physical devices.
About Single – level Directory
- This is the simplest of the directory structures.
- All files are stored in the same directory itself because it is quite easy to understand as well as support.
- The first computer of the world i.e., the CDC 6600 also operated on just one directory and it could be used by a number of users at the same time.
- There are significant limitations of the single-level directory.
- These limitations come in to play when there are more than one users using the system or when the system has to deal with a large number of files.
- All the files have to be assigned unique names since they are all stored under the same directory.
- No two files can have the same file name.
- It may become difficult to keep the names of the files in mind if they are large in number.
About Two–level Directory
- The limitations of the single level directory structure can be overcome by creating an individual directory for every user.
- This is the most standard solution for the problems of the single level directories.
- In this two-level directory structure, a UFD or user file directory is made for every user.
- The structure of all the user file directories is almost the same, but the difference is that only the files of the individual user are stored in one.
- When a user tries to log in or when he starts a task, the system searches for the MFD or master file directory.
- The name of the user or his/ her account number is used for indexing the MFDs in the operating system.
- Each of those entries points to the UFD belonging to that user.
- When a reference is made to some file, the system only searches for the user file directory for example, when a file has to be deleted or created.