File Management - Information Technology - Lecture Slides, Slides of Information Technology

Download File Management - Information Technology - Lecture Slides and more Slides Information Technology in PDF only on Docsity!

Topic

File

Management

Index

-^

Definition

of

OS

-^

File

and

related

terms

-^

Purpose

of

File

Management

-^

Operations

on

File

-^

File

Allocation

Methods

-^

File

Organization

Functions

of

OS

•^

Process

Management

•^

Memory

Management

•^

I/O

Management

•^

Secondary

Storage

Management

•^

File

Management

What

is

File

•^

A file is a collection of related informationdefined by its creator.

-^

Files represent programs (both source andobject forms) and data.

Information

structure

of

a

file

-^

the

fi

le’s

type

(plain

fi

le,

directory,

etc),

the

fi

le’s

size,

in

bytes

and/or

blocks,

any

limits

set

on

the

fi

le’s

size,

the

primary

owner

of

the

fi

le,

information

about

other

potential

users

of

this

fi

le,

access

constraints

on

the

owner

and

other

users,

dates

and

times

of

creation,

last

access

and

last

modi

fi

cation,

dates

and

times

of

last

backup

and

recovery,

and

event

triggers

when

the

fi

le

changes

Terms

Used

with

Files

•^

Field^ –

Basic

element

of

data

Contains

a

single

value

Characterized

by

its

length

and

data

type

•^

Record^ –

Collection

of

related

fields

Treated

as

a

unit

-^

Example:

employee

record

File

Management

•^

The operating system is responsible for thefollowing activities in connections with filemanagement:^ ⎯

File creation and deletion. ⎯^

Directory creation and deletion. ⎯^

Support

for

manipulating

files

and

directories. ⎯^

Mapping files onto secondary storage. ⎯^

File backup on stable (nonvolatile) storagemedia.

File

Management

• Identify and locate a selected file• Use a directory to describe the location of all

files plus their attributes

• On a shared system describe user access

control

• Blocking for access to files• Allocate files to free blocks• Manage free storage for available blocks.

Purpose

of

File

Management

•^

provide simple and fast algorithms to read andwrite files

-^

give and deny access rights on files to usersand programs

-^

allocate and deallocate files to processes

-^

provide

users

and

programs

with

simple

commands for file handling

Minimal

Set

of

Requirements

•^

Each user should be able to create, delete,read, write and modify files

-^

Each user may have controlled access to otherusers’ files

-^

Each user may control what type of accessesare allowed to the users’ files

-^

Each user should be able to restructure theuser’s files

File

Operations

•^

Create

•^

Delete

•^

Open

•^

Close

•^

Read

•^

Write

Typical

Operations

-^

Retrieve_All

: Retrieve all the records of a file.

This operation will be required for an applicationthat must process all the information in the file atone time.

-^

Retrieve_One

:^

This

operation

requires

the

retrieval

of

just

a^

single

record.

Interactive,

transaction

‐oriented

applications

need

this

operation

-^

Retrieve_Next

:^

This

operation

requires

the

retrieval of the record that is “next” in somelogical sequence to the most recently receivedrecord. for example : filling in forms

Typical

Operations

•^

Update_One :

Retrieve a record, update one

or more of its fields, and rewrite updatedrecord back into the file.

-^

Retrieve_Few :

Retrieve a number of records.

For

example,

an

application

may

wish

to

retrieve all records that satisfy a certain set ofcriteria.

Access

Rights

•^

None^ –

User may not know of the existence of thefile

User

is

not

allowed

to

read

the

user

directory that includes the file

•^

Knowledge^ –

User can only determine that the file existsand who its owner is