Chapter 1 Introduction to Operating System Concepts

Chapter 1 :
Introduction to Operating System
Concepts.
Meenal K Jabde
Modern College of Arts, Science &
Commerce Ganeshkhind, Pune 16

Contents
1.Introduction to Operating System Concept.
2. Different services provided by Operating System
to User.
3. Introduce the concept of Process, Process States,
Process Control Block, User Interface, System Calls.

What is Operating System?
 An operating system is a program that controls the
execution of application programs and acts as an
interface between the user of a computer and the
computer hardware.
 A more common definition is that the operating system
is the one program running at all times on the computer
(usually called the kernel), with all else being
application programs.

Functions of Operating system – Operating
system performs three functions:
• Convenience: An OS makes a computer more convenient
to use.
• Efficiency: An OS allows the computer system resources
to be used efficiently.
• Ability to Evolve: An OS should be constructed in such a
way as to permit the effective development, testing, and
introduction of new system functions at the same time
without interfering with service.

The operating system as User Interface –
User
System and application programs
Operating system
Hardware

Conceptual view of a computer system

OS is designed
to serve two
basic purposes
 It controls the allocation and use of the
computing System’s resources among
the various user and tasks.
 It provides an interface between the
computer hardware and the programmer
that simplifies and makes it feasible for
coding, creation, debugging of
application programs.

The Operating system must support the following tasks.
The task are:
Provides the facilities to create, modification of programs and data files using an editor.
Access to the compiler for translating the user program from high-level language to
machine language.
Provide a loader program to move the compiled program code to the computer’s memory
for execution.
Provide routines that handle the details of I/O programming

History of Operating system
Generation Year Electronic device used Types of OS Device
First 1945-55 Vacuum Tubes Plug Boards
Second 1955-65 Transistors Batch Systems
Third 1965-80 Integrated Circuits(IC) Multiprogramming
Fourth Since 1980 Large Scale Integration PC

Types of
Operating
Systems
An Operating System performs all the basic tasks like managing files,
processes, and memory. Thus operating system acts as the manager of all the
resources, i.e., resource manager. Thus, the operating system becomes an
interface between user and machine.
Some widely used operating systems are as follows-
Batch Operating System- Sequence of jobs in a program on a computer
without manual interventions.
Time-sharing operating System- allows many users to share the computer
resources. (Max utilization of the resources).
Distributed operating System- Manages a group of different computers and
makes appear to be a single computer.
Network operating system- computers running in different operating systems
can participate in a common network (It is used for security purposes).
Real-time operating system – meant applications to fix the deadlines.

1. Batch Operating System –
This type of operating system does
not interact with the computer
directly. There is an operator which
takes similar jobs having the same
requirement and group them into
batches. It is the responsibility of the
operator to sort jobs with similar
needs

2. Time-Sharing Operating Systems –
Each task is given some time to execute so
that all the tasks work smoothly. Each user
gets the time of CPU as they use a single
system. These systems are also known as
Multitasking Systems. The task can be from a
single user or different users also. The time
that each task gets to execute is called
quantum. After this time interval is over OS
switches over to the next task.

3. Distributed Operating System –
These types of the operating system is a recent
advancement in the world of computer technology
and are being widely accepted all over the world
and, that too, with a great pace. Various autonomous
interconnected computers communicate with each
other using a shared communication network.
Independent systems possess their own memory unit
and CPU.

4. Network Operating System –
 These systems run on a server and
provide the capability to manage data,
users, groups, security, applications, and
other networking functions. These types
of operating systems allow shared access
of files, printers, security, applications,
and other networking functions over a
small private network.

5. Real-Time Operating System –
 These types of OSs serve real-time systems. The time
interval required to process and respond to inputs is very
small. This time interval is called response time.
 Real-time systems are used when there are time
requirements that are very strict like missile systems, air
traffic control systems, robots, etc.

Two types of Real-Time Operating System which are
as follows:
 Hard Real-Time Systems:
These OSs are meant for applications where time
constraints are very strict and even the shortest
possible delay is not acceptable. These systems are
built for saving life like automatic parachutes or
airbags which are required to be readily available in
case of any accident. Virtual memory is rarely found
in these systems.
 Soft Real-Time Systems:
These OSs are for applications where for time-
constraint is less strict.

A list of common
services offered
by an almost all
operating
systems:
User Interface
Program Execution
File system manipulation
Input / Output Operations
Communication
Resource Allocation
Error Detection
Accounting
Security and protection

Process
 A process is a program in execution. For example, when we write a
program in C or C++ and compile it, the compiler creates binary code. The
original code and binary code are both programs. When we run the binary
code, it becomes a process.
 A process is an ‘active’ entity, as opposed to a program, which is a
‘passive’ entity. A single program can create many processes when run
multiple times; for example, when we open a .exe or binary file multiple
times, multiple instances begin (multiple processes are created).

What does a process look like in
memory?
 Text Section: A Process, sometimes known as
the Text Section, also includes the current
activity represented by the value of the Program
Counter.
 Stack: The stack contains the temporary data,
such as function parameters, returns addresses,
and local variables.
 Data Section: Contains the global variable.
 Heap Section: Dynamically allocated memory to
process during its run time.

Attributes or Characteristics of a Process
 1. Process Id: A unique identifier assigned by the operating system
 2. Process State: Can be ready, running, etc.
 3. CPU registers: Like the Program Counter (CPU registers must be
saved and restored when a process is swapped in and out of CPU)
 4. Account's information:
 5. I/O status information: For example, devices allocated to the process,
open files, etc
 6. CPU scheduling information: For example, Priority (Different
processes may have different priorities, for example a
short process may be assigned a low priority in the shortest job first
scheduling)

Process Life Cycle/States of Process
 1. New: Newly Created Process (or) being-created
process.
 2. Ready: After creation process moves to Ready state,
i.e. the process is ready for execution.
 3. Run: Currently running process in CPU (only one
process a time can be under execution in a single
processor).
 4. Wait (or Block): When a process requests I/O access.
 5. Complete (or Terminated): The process completed its
execution.
 6. Suspended Ready: When the ready queue becomes
full, some processes are moved to suspended ready
state
 7. Suspended Block: When waiting queue becomes
full.

Process Control Block
 A Process Control Block is a data structure maintained
by the Operating System for every process. The PCB is
identified by an integer process ID (PID). A PCB keeps
all the information needed to keep track of a process as
listed below in the table.
 While creating a process the operating system performs
several operations. To identify the processes, it assigns
a process identification number (PID) to each process.
As the operating system supports multi-programming,
it needs to keep track of all the processes. For this task,
the process control block (PCB) is used to track the
process’s execution status.

1. Pointer – It is a stack pointer which is required to be saved when the
process is switched from one state to another to retain the current position of
the process.
2. Process state – It stores the respective state of the process.
3. Process number – Every process is assigned with a unique id known as
process ID or PID which stores the process identifier.
4. Program counter – It stores the counter which contains the address of the
next instruction that is to be executed for the process.
5. Register – These are the CPU registers which includes: accumulator, base,
registers and general-purpose registers.
6. Memory limits – This field contains the information about memory
management system used by operating system. This may include the page
tables, segment tables etc.
7. Open files list – This information includes the list of files opened for a
process.
8. Miscellaneous accounting and status data – This field includes information
about the amount of CPU used, time constraints, jobs or process number, etc.

What are system calls in
Operating System?
 The interface between a process
and an operating system is
provided by system calls. In
general, system calls are available
as assembly language instructions.
They are also included in the
manuals used by the assembly
level programmers. System calls
are usually made when a process
in user mode requires access to a
resource. Then it requests the
kernel to provide the resource via
a system call.

Types of System Calls
There are mainly five types of system calls.
Process Control
These system calls deal with processes such as process creation, process termination etc.
File Management
These system calls are responsible for file manipulation such as creating a file, reading a file, writing
into a file etc.
Device Management
These system calls are responsible for device manipulation such as reading from device buffers,
writing into device buffers etc.
Information Maintenance
These system calls handle information and its transfer between the operating system and the user
program.
Communication
These system calls are useful for interprocess communication. They also deal with creating and
deleting a communication connection.

Types of System Calls Windows Linux
Process Control
CreateProcess()
ExitProcess()
WaitForSingleObject()
fork()
exit()
wait()
File Management
CreateFile()
ReadFile()
WriteFile()
CloseHandle()
open()
read()
write()
close()
Device Management
SetConsoleMode()
ReadConsole()
WriteConsole()
ioctl()
read()
write()
Information Maintenance
GetCurrentProcessID()
SetTimer()
Sleep()
getpid()
alarm()
sleep()
Communication
CreatePipe()
CreateFileMapping()
MapViewOfFile()
pipe()
shmget()
mmap()

Chapter 1 Introduction to Operating System Concepts

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Chapter 1 Introduction to Operating System Concepts