Introduction to OS and RTOS concepts

1. Introduction to
Operating systems & RTOS
Dr. Y.NARASIMHA MURTHY. Ph. D
yayavaram@yahoo.com

2. Invocation….
Where the mind is without fear and the head is held high;
Where knowledge is free;
Where the world has not been broken up
into fragments by narrow domestic walls;
Where words come out from the depth of truth;
Where tireless striving stretches its arms towards perfection;
Where the clear stream of reason
has not lost its way into the dreary desert sand of dead habit;
Where the mind is led forward by thee into ever-widening
thought and action---
Into that heaven of freedom, my Father, let my country awake.
----RABINDRANATH TAGORE

3. • A computer is a complex system with many
resources like CPU, I/O devices, disk, memory
etc… For any common user it is always a
confusion about the using of the resources
effectively.
• Because, unless otherwise the system is user-
friendly, the user cannot use the computers
effectively.

4. contd
So we always require a system software which can
take care of all the hardware complexities and
shoulder the responsibility of resource allocation
such that the user can work with the computer
more effectively.
This was realised by the people very long back and
they tried to develop a software to shield the
programmers from the complexity of the
hardware.

5. The result is, a layer of software on the top
of the hardware, to manage all parts of the
system and present the user with an interface
or “Virtual machine” that is easier to
understand the program. This layer of the
software has become our so-called
OPERATING SYSTEM.

6. Now Lets answer the question
What is an Operating System?

7. A more formal definition!
OS is “A collection of software modules to assist
programmers in enhancing the system efficiency ,
flexibility and robustness.
Or
“Operating system is a piece of software which
controls all the computer’s resources and provides
the base upon which the application programs can
be written”

8. From the user point of view
OS is “ An extended machine (virtual)”
and
From the systems view point
“It is a resource manager”.

9. Let us substantiate !
 The operating system shields the
programmer from the disk hardware and
provides a simple file oriented interface. It
also conceals a lot of unpleasant business
concerning interrupts, timers, memory
management and other low level features.
So the function of the OS is to present the
user with the equivalent of an extended
machine or virtual machine.

10. Contd……
 A computer is provided with processors,
memories, timers, disks, terminals, drives, printers,
network interfaces and a wide variety of the other
devices. The operating system provides an
orderly and controlled allocation of the
processors, memories and I/O devices among the
various programs competing for them. It also
keep track of, who is using which resource, to
grant resource requests, to account for usage and
to mediate conflicting requests from different
users and programs.

11. Contd….
Provides an environment in which
programs can be executed. Makes efficient
use of computer hardware and peripherals.
Hide the peculiarities of the disks and
other I/O devices.Hence the OS is also
treated as a resource manager

12. So,Where your OS sits in your System?
compilers
databases
word
processors
CPU
memory
I/O devices

13. Evolution of OS
 The next slide shows the evolution of OS .
 Actually Prof.E.W.Dijsktra is considered as the
father of Operating system.

14. Generation Era O/S used Feature
First 1945-55
Vacuum tubes
ENIAC
EDVAC
Analog
computers
No O/S Plug in boards
Jumper wired
Second 1955-65
IBM 1401, 7094
Batch O/S (Not interact
system)
Paper tape
Punched cards
Offline printing
Third 1965-80
IBM 360
Time sharing O/S (many at
the same time PDP-II
Spooling (On-line)
Multiprogramming
Fourth 1980-90
IBM 360
MS-DOS
UNIX
User friendly. He
need not know
about computer
Fifth 1990 KBCS
(Knowledge
based computer
system)
Distributed O/S
Network O/S
More advanced

15. The basic requirements of OS:
 Usability (Robustness)
OS should accept all valid inputs ,even with errors
and gracefully handle all invalid inputs .It should
not be crashed under any circumstances ,and
could be recovered,even we remove any
hardware while they are running .

16. It should provide every facility for the efficient
development of application software and should
not leave out any part of the facility.
Adaptability :
Should support necessary activities,and not
to impose unnecessary restrictions.Adapt as
needs and resources change.
Facilities:

17. Cost:
Low maintenance cost and the system should
not require constant attention.Efficient
service and good algorithms must be
provided at low cost

18. OS Components
 Kernel: Core components of the OS
 Process scheduler :
 Determines when and for long each process executes
 Memory manager :
 Determines when and how memory is allocated to processes
 Decides what to do when main memory is full
 File system :
 Organizes named collections of data in persistent storage
 Networking :
 Enables processes to communicate with one another

19. The primary functions of an
operating system
 Multiplexing the processor(s)
 Scheduling the processes
 Coordinating interaction among processes,interprocess
communication and Synchronization.
 Managing the system resources(I/O,memory,data files)
 Enforcing acess control and protection
 Maintaining the system integrity and performing error
recovery
 Providing an interface to the users

20. TYPES OF OPERATING SYSTEMS
There are three types of Operating systems based
on their application
• Stand-Alone Operating system
• Network Operating systems
• Embedded Operating systems

21. Stand-Alone Operating system
 It is a complete operating system that works
on a desktop or notebook computer.
Examples of stand-alone operating systems are:
 DOS
 Windows 2000 professional
 Mac OS X

22. Network Operating systems
 It is an operating system that provides extensive
support for computer networks. A network
operating system typically resides on a server.
Examples of a network Operating system are:
 Windows 2000 server
 Unix
 Linux
 Solaris

23. Embedded Operating system
 You can find this operating system on handheld
computers and small devices. It resides on a
ROM chip. Examples of embedded operating
systems are :
o Windows CE
o Pocket PC 2002
o Palm OS

24. Now Lets see various Operating
systems and their features

29. contd

30. contd

31. contd

32. contd

33. contd

34. contd

35. contd

36. contd

58. Operating systems market share
S.No Operating system Market share
1
2
3
4
5
6
7
8
9
10
11
Windows XP
Windows Vista
Windows 2000
Mac OS
MacIntel
Windows 98
Linux
Windows NT
Windows Me
Ninendo Wii
Other
81.94%
4.52%
4.00%
3.52%
2.48%
1.14%
0.71%
0.66%
0.59%
0.17%
0.20%

59. REAL- TIME OPERATING SYSTEM
(RTOS)
 “The ability of the operating system to
provide a required level of service in a
bounded response time”.
Or
 The Real time operating system is an
operating system that make it suitable for
building real time computing applications
also known as real time systems(RTS).

60. What is a real time system(RTS)?
A RTS is a system where correctness of computing
depends not only on the correctness of the logical
result of the computation but also on the result of
delivery time. In a well designed RTS each individual
dead line should be met. But in practice it is not
possible and also costly to achieve this requirement.
So, people classified the real time systems in to the
following types.

61. Hard Real time
Here missing an individual deadline results in
catastrophic failure of the system which also
causes a great financial loss .
The examples for Hard real time systems are:
 Air traffic control
 Nuclear power plant control

62. Firm Real time
In this, missing a deadline results in
unacceptable quality reduction. Technically
there is no difference with hard Real time, but
economically the disaster risk is limited.
Examples for Firm real time are :
o Failure of Ignition of a automobile
o Failure of opening of a safe

63. Soft real time
Here the dead line may not be fulfilled and can be
recovered from. The reduction in system quality
and performance is at an acceptable level.
Examples of Soft real time systems :
 Multimedia transmission and reception
 Networking, telecom (Mobile) networks
 websites and services
 Computer games

64. Components of an RTOS
 Process (task) management
 Scheduler
 Synchronization mechanism
Interprocess communication (IPC)
Semaphores
 Memory management
 Interrupt service mechanism
 I/O management , H.A.Layer
 Development Environments
 Communication subsystems (Option)
 Board Support Packages (BSP)

65. Features of RTOS’s
 Predictability
 Timeliness
 Reliability
 Fault tolerant
 Efficiency of System
Components
 Resource Allocation.
 Interrupt Handling.
 Other issues like kernel
size.

66. Types of RTOS
Commercial RTOSs
 VxWorks
 QNX
 MicroC/OS-II
 RTLinux
 Windows CE ( www.microsoft.com)

67. VxWorks
 This is from Wind River (www.windriver.com).
 One of the most popular real time operating
system
 This has been used in the Mars pathfinder
 It supports a number of processors including
Power Pc, Intel strong ARM,ARM,Hitachi
SuperH, Motorola ColdFire etc…
 It supports multiple scheduling algorithm and
also priority inheritance

68. QNX Neutrino
 It is a popular real time operating system from QNX
software systems limited (www. qnx.com)
 It supports a number of Processors namely
ARM,MIPS,Power PC,SH-4,X86 &Pentium…
 It has support for C,C++ and Java languages and TCP/IP
protocol stack.
 This supports multiple scheduling algorithms and up to
65,535 tasks. My SQL can be integrated with this OS to
create embedded database applications.
 Even small embedded systems can use this OS as it
requires 64K Kernel ROM and 32K kernel RAM.

69. MicroC/OS-II
 Microcontroller operating system version –II is
developed by Jean J.Labrosse(www.ucos-
II.com)is a preemptive real-time operating
system which is popular in academic institutions
for teaching RTOS concepts.
 It can support only 64 tasks out of which eight
are system tasks
 Round-robin scheduling algorithm is not
supported by this OS

70. RTLinux
 This OS was developed by FSM
Labs(www.fsmlabs.com) and available in two
versions RTLinux Pro and RTLinuxFree.
 The RTLinux Pro is the priced edition and
RTLinux Free is the free open source release.
 RTLinux is a hard real-time operating system
with support for many processors such as
x86,Pentium,PowerPC,ARM,Fujitsu,MIPS and
Alpha
 It does not support priority inheritance.

71. Windows CE
 Windows CE (also known officially as Windows
Embedded Compact and sometimes
abbreviated WinCE) is an operating system
developed by Microsoft for minimalistic
computers and embedded systems.
 Windows CE is optimized for devices that have
minimal storage—a Windows CE kernel may
run in under a megabyte of memory

72.  The system supports 256 priority levels and uses
priority inheritance for dealing with priority
inversion. The fundamental unit of execution is
the thread. This helps to simplify the interface
and improve execution time.
 A distinctive feature of Windows CE compared
to other Microsoft operating systems is that
large parts of it are offered in source code form.

73. Programming languages Used
 C is most widely used in RTOS programming
 C++ and Ada are the next more popular for large
projects.
 Assembly languages for increasing efficiency and
reusing the previous code
 Java may also be a choice for some applications

74. Which is the Best?
 It is always very difficult to judge which RTOS
is the best and which is the worst.It depends on
the application and interests of the user. Among
the above, Linux is royalty free but it has serious
drawbacks if it comes to real-time behavior. The
VxWorks is a very old and stable RTOS.
Similarly Windows CE 5.0 version RTOS is a
robust and stable regarding the real-time
behavior.

75. REFERENCES
 Modern Operating Sytems- Andrew S. Tanenbaum (PHI)
 Operating Systems –W. Stallings (PHI)
 Operating system Concepts-Avi Silberschatz & Peter
Baer Galvin.
 Operating Systems-D. M. Dhamdhere- TMH