This is an PPT of Operating System. It include the following topic "File System in Operating System ".

1. Presented By:
Apoorva Nagar
MCA/25013/18

2. FILE SYSTEM
 Computer user stores program and data in file so that
they can be used conveniently and preserved across
computing session.
 Operating system organise the file management into two
components: File system
Input-output control system(IOCS)
File Processing
 This term is used to describe the general sequence of
opening the file,reading the file or writing in file and
closing of file.
 File system locate the file using directory structure
which is the arrangement of many directories.

3. File system
 A file system views the file as a collection of data
that is owned by the user and can be shared with
authorised users.
 File system provides protection of files from illegal
access.
 It provides directory structure for convenient
grouping of files.
 It provides file sharing semantics for concurrent
accesses to a file.
 It provides reliable storage of file.

4. Input-Output Control System
 The IOCS views a file as a repository of data that
need to be accessed speedily and are stored in a I/O
device that need to be used efficiently.
 IOCS policies ensures efficient operation of I/O
devices and efficient file processing through
mechanism modules.
 These mechanism modules in turn invoke kernel
through system calls.
 It provides efficient access to data in a file.

5. FILES AND FILE OPERSTIONS
 A file system houses and organises different types of
files like data files,executable programs, video clips,
photos etc.
 These file types are grouped into two classes:
Structured files
Byte stream files
 A structured file is a collection of records which are
collection of fields which contains a single data
item.
 Byte stream file is “flat” that is there are no records
and fields in it.

6. OPERATIONS ON FILES

7. FUNDAMENTAL FILE ORGANISATIONS
File organisation is a combination of two features- method
of arranging records in the file and a procedure to access
them.
Sequential File Organisation
 In this records are stored in an ascending or descending
sequence according to the key field.
 It supports two kind of action-read the next record and
skip the next record.
Direct File Organisation
 It provides convenience and efficiency of file processing
when records are accessed in random order.
 Records are accessed through direct-access files where
in read/write command needs to mention value in key
field

8. Index Sequential File Organisation
 An index helps to determine the location of a record
from its key value.
 Index of a file contains an index entry with the
format
(key value, disk address) for each key value in
file.
 Index Sequential File Organisation is a hybrid
organisation that combines elements of the indexed
and the sequential file organisation.

9. DIRECTORIES
 A directory contains the information about a group of
files.
 Fields in Directory Entry:

10. Directory Tree
 Most file system contains the feature that allow the
user to create new directory,give it a name of user
choice and create other directories and files in it
upto user desired level. The resulting directory
structure is called directory tree.
 File system provides a directory called root that
contains the home directory of each user.
Operations On Directories
 Searching
 Maintenance operations like creating/deleting
files,updating file entries, listing file entries,
deleting directories.

11. ORGANISATION OF DIRECTORIES
When directories contains large number of entries Hash
tables and B+ tree are used.
Hash Table Directory
 A directory can be maintained using hash table
organisation Hash with opening address.
 When new files are created hash function h is applied
which yield entry number e.
 To find unused entry, entries given by (e+1)mod(n) is
checked repeatedly. n is size of hash table
B+ Directory
 In a B+ directory information about files are recorded
only in leaf node of the tree.
 Non leaf nodes contains index entries and are used
merely to direct the search to appropriate part of the
tree.
 It has the capability of fast search.