Os functions

Definition
 Operating system is a system software that controls
the hardware of the computer system and provides an
environment for interaction between the user and
system.
 Simply OS(Operating System) is an intermediary
between user and computer hardware.

Roles of OS
 The roles played by the OS can be summarized as
follows:-
 Resource manager:-Provides efficient, easy and
systematic utilization of the resources.
 Service provider:-Provides an environment for
smooth execution of the other programs of the user.
 Interface:-Provides an interface(GUI or DOS) to the
user of the computer system.
 Examples of OS:-MS-DOS,MS95/98/XP/Vista/7/8,
 UNIX, LINUX, Solaris, OS/2 and Mac OS.

Functions of Operating System
 Following are the functions of operating system:
1. Process Management
2. Memory Management
3. File Management
4. Device Management
5. Security

Process Management
 Process Management:- In computer system several
processes are running at the same time on the CPU,
for maximum utilization of CPU. So these all
processes are to be properly scheduled to get CPU for
execution. OS uses scheduling algorithms for that
 Processes are require several resources for execution
OS must provide them.
 New, ready, running, waiting, finished are states of
process.

Memory Management
 In multiprogramming environment main memory is
very precious resource, so memory management is
one of the very important function of OS.
 The OS works as memory manager.
The OS ensures the following:
1. Allocation of enough memory space to the individual
processes & data at their execution time.

2. Optimum use of all kind of available memories.
3. Release of data & processes from the memory once
the process is completed.

Methods of memory allocation
Contiguous: -Contiguous memory chunks(Blocks)
are allocated to the different processes
a. Fixed partition
b. Variable or Dynamic

FIXED PARTITION
40 OS
40
40
40
40 OS
20
20
A
40
40
40 OS
20
20
A
30 B
10
40
40 OS
20
20
A
30 B
10
40 C

Internal Fragmentation
 In fixed partition , the process occupies an entire
partition and the unused part of the memory cannot be
utilized for other processes.
 The unused part is wasted and this problem is called
internal fragmentation.

VARIABLE PARTITION
30 OS 30 OS
20 A
30 OS
20
30
A
B
30 OS
20
30 B
60 C
10
30 OS
20
30 B

Continue……
1.As the process A arrives, the chunks of 20KB is
allocated to A.
2.Then the process B arrives, the chunk of 30KB is
allocated to B.
3. Now the process A is completed so 20KB of A is
released as shown in figure.
4. When process C arrives, the chunk of 60KB is
allocated to process C as shown in figure, because it
does not fit in the recently released 20KB of A and the
total memory of 150KB is divided into chunks of
varying size ranging from 10KB to 60Kb.

External fragmentation.
 If total memory is available to accommodate a
requesting process, But OS is not allowed this process
because this total memory part is not contiguous. The
total memory part is available into many different
chunks. This problem is called External
fragmentation.

File management
 A file is a collection of logically related information which
can be stored in the memory of the computer system and
can be read, write and manipulated.
 The OS performs following operations on the file such
1. Creating the file
2. Deleting the file
3. Searching the file
4. Renaming the file
5. Updating the file

Continue……….
 Characteristics of a file:
1. Name
2. Location
3. Size
4. Type
5. Date (of last access and creation, modification)
6. Time

 Device management:
1. -OS is responsible for effective utilization of various
I/O devices.
2. A device manager in the OS handles the
management of the devices connected to the
computer system.
3. OS communicate with the devices through a device
driver software.
4. The devices are connected to the computer bia
different ports.

 Security:-OS protects our system from different kind
of external threats.
1. OS provides facility of creating different users, these
users are password protected. So, only the user with
the valid password can use the account
2. The OS provides sharing of folders and drives on
network. We can set access permissions to users on
network.

Types of operating systems
Batch operating system:-In this OS a job pool is
created by operator according to the need of users,
than operator loads the job pool into the main memory
and CPU executes the job one by one. These are very
slow operating systems. They require trained operator
to load jobs into memory and to take results.
Sometime CPU sits idle when jobs are busy with
input/output.

 Multiprogramming OS:-In this systems multiple
processes are allowed to reside in main memory, so
CPU can select one of them if currently executing
process is want to do I/O. In this system CPU is never
sits idle. A scheduler select and deselect processes
during execution. These systems are fast.
 WIN-98/XP/7

Time sharing OS:-This is logical extension of
multiprogramming OS. CPU switching among
processes are very fast, so that each user can execute
his/her program without delay. These are also called
multitasking OS.
Windows NT/2000/XP

 Real Time OS:-They are designed for handling real
time applications, where quick response in minimum
time is very essential. For example, to withdraw
money from your nearest ATM, operations of military
instruments, traffic control system, online bookng
systems etc.
 IBM’s OS-9, LINUX, OS/390

 Network operating system:- These OS provide
networking facilities like one can share data and
printer on network.
 These computer communicate with each other through
communication lines.
 These OS are designed to install as a server for clients
on network.
 WINDOWS server 2003 and LINUX are easily
configured as a server.

Os functions

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