This is the module of the Operating System that is
responsible for creating and/or deleting files in the file system and managing the
input and output of data in the file system.
File System
A File System refers to the arrangement in a secondary
storage that is done by the Operating System for the purpose of data storage
and retrieval. The File System of any two Operating Systems is not identical. The
following are the names of the Operating Systems and the respective file
systems that they follow.
·
DOS : FAT File System
·
Windows 9x : VFAT
·
Windows XP/NT/2000/2003 : NTFS
·
Windows Vista : NTFS
·
UNIX : UFS (UNIX File
System)
·
Linux : Ext II File System
Note: Windows Vista is now built on the NTFS file system. Windows
Future Storage (WinFS), a relational database based data storage engine, is
currently under development and will be introduced later as a free add-on for
Windows Vista in late 2006.
Root File System
The Root File System specifies the information related to
the files on the disk or the secondary storage. Typical contents include the
following.
·
Name of the file
·
Starting Cluster Number
·
Size of the file
·
Date and Time stamp
·
File Permissions
File Control Block
A File Control Block (FCB) is a data structure that contains
information related to the files that are present on a File System. Even
though the contents of the FCB would vary from one Operating System to another,
the following are the common parts that it contains.
·
Name of the file
·
Location
·
Size of the file
·
Date and Time stamp
Disk Fragmentation and De-Fragmentation
The files created in the secondary storage are created and
deleted as needed. Allocation of the clusters for a file in the file system is
non–contiguous. The Operating System maintains a free cluster list to keep
track of the clusters that are available for use or re-use. Due to deletions
of one or more files in the file system, the clusters that are allocated to a
file are not in sequence, but rather they are scattered all over the disk with
free clusters or holes in between. This concept is known as disk
fragmentation. The disk de-fragmentation tools available are responsible for
compacting or arranging the clusters of a file contiguously in the disk.