Thorsten LaMarr

The advantages of using a file system include the:

Disadvantages of using a file system include:

A file is a collection of related information that is recorded on secondary storage. Or file is a collection of logically related entities. From the user’s perspective, a file is the smallest allotment of logical secondary storage.

The name  of the file is divided into two parts as shown below:

FILE DIRECTORIES: Collection of files is a file directory. The directory contains information about the files, including attributes, location and ownership. Much of this information, especially that is concerned with storage, is managed by the operating system. The directory is itself a file, accessible by various file management routines.

Information contained in a device directory are:

Operation performed on directory are:

Advantages of maintaining directories are:

SINGLE-LEVEL DIRECTORY In this a single directory is maintained for all the users.

TWO-LEVEL DIRECTORY In this separate directories for each user is maintained.

TREE-STRUCTURED DIRECTORY : Directory is maintained in the form of a tree. Searching is efficient and also there is grouping capability. We have absolute or relative path name for a file.

FILE ALLOCATION METHODS :

1. Continuous Allocation –A single continuous set of blocks is allocated to a file at the time of file creation. Thus, this is a pre-allocation strategy, using variable size portions. The file allocation table needs just a single entry for each file, showing the starting block and the length of the file. This method is best from the point of view of the individual sequential file. Multiple blocks can be read in at a time to improve I/O performance for sequential processing. It is also easy to retrieve a single block. For example, if a file starts at block b, and the ith block of the file is wanted, its location on secondary storage is simply b+i-1.

Disadvantage –

2. Linked Allocation(Non-contiguous allocation) –Allocation is on an individual block basis. Each block contains a pointer to the next block in the chain. Again the file table needs just a single entry for each file, showing the starting block and the length of the file. Although pre-allocation is possible, it is more common simply to allocate blocks as needed. Any free block can be added to the chain. The blocks need not be continuous. Increase in file size is always possible if free disk block is available. There is no external fragmentation because only one block at a time is needed but there can be internal fragmentation but it exists only in the last disk block of file.

Disadvantage –

3. Indexed Allocation –It addresses many of the problems of contiguous and chained allocation. In this case, the file allocation table contains a separate one-level index for each file: The index has one entry for each block allocated to the file. Allocation may be on the basis of fixed-size blocks or variable-sized blocks. Allocation by blocks eliminates external fragmentation, whereas allocation by variable-size blocks improves locality. This allocation technique supports both sequential and direct access to the file and thus is the most popular form of file allocation.

Disk Free Space Management :

Just as the space that is allocated to files must be managed ,so the space that is not currently allocated to any file must be managed. To perform any of the file allocation techniques,it is necessary to know what blocks on the disk are available. Thus we need a disk allocation table in addition to a file allocation table.The following are the approaches used for free space management.

This article is contributed by Aakansha yadav

If you have dry skin, apply moisturizer while your skin is still damp This helps to trap moisture and keep your skin soft and smooth You might think that

You have to have an understanding of Git before you can understand it.The person who created Linux is the same person who started Git.Git is similar to other versions.What is Git, aversion control system?Up to and after the first official non-beta release, developers make constant changes to the code and release new versions.

Is this correct?

Mailed in a mini Nike shoebox, this gift card unlocks a world of footwear, apparel, and equipment Gift Cards are redeemable at Nike com, Conversecom,