Directory Implementation

Directory Implementation

• Directory is implemented by using linear list and hash table. 

Linear list

• Linear list is simple method of directory implementation. It uses file names with bead pointers to data block. It is time consuming because of searching overheads.

• To create a new file, file name is searched in the directory to avoid the file name duplication. Then it adds new entry at the end of the directory. To delete a file, again file name is searched in the directory. Space is released after deleting a file. Directory entry is also removed. Unused space is marked as free entry. Last entry of directory is copied into the free space list.

• For deleting a file, some OS uses linked list. Linked list decreases time required.

• Searching the directory entry is the major disadvantage. It is slow process. Because of this reason, many operating system uses software cache memory. It stores the most recently used directory information.

Hash table

• Hash table is one more data structure used for directory implementation. Hash table takes a value computed from the file name and returns a pointer to the file name in the liner list.

• Hash table reduces the searching time. It uses fixed size block.