An operating system is software that manages computer resources and provides services to application programs. It sits between the computer hardware and application software. There are three main types of operating systems: stand-alone, network, and embedded. Real-time operating systems (RTOS) are designed for applications with time-critical deadlines like process control. Key features of an RTOS include short and predictable context switching, interrupt handling times, and inter-process communication. Popular RTOS include VxWorks, QNX, and RTLinux.

2. What is an Operating System?

3. A more formal definition!
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

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

5. TYPES OF OPERATING SYSTEMS
Stand-Alone Operating system
Network Operating systems
Embedded Operating systems

6. 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

7. 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

8. 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 :
oWindows CE
oPocket PC 2002
oPalm OS

9. What is RTOS?
A real-time operating system (RTOS) that supports
real-time applications and embedded systems.
Real-time applications have the requirement to meet
task deadlines in addition to the logical correctness
of the results.
Multiple events handled by a single processor
Events may occur simultaneously
Processor must handle multiple, often competing events

11. Difference between a General purpose
operating system(GPOS) and an RTOS
A GPOS is used for systems/applications that
are not time critical.
In the case of a GPOS – task scheduling is not
based on “priority”,it is programmed to achieve
high throughput
A GPOS is made for high end, general purpose
systems whereas RTOS is usually designed for a
low end, stand alone device
All the process and threads in RTOS has got
bounded latencies – which means –a process/thread
will get executed within a specified time limit
.

12. Classification real time systems(RTS)
Hard Real Time System
Firm Real Time System
Soft Real Time System

13. 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

14. 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 :
Failure of Ignition of a automobile
Failure of opening of a safe

15. 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

16. Features of an RTOS:
•Context switching latency should be short. This
means that the time taken while saving the
context of current task and then switching over to
another task should be short.
•The time taken between executing the last
instruction of an interrupted task and executing
the first instruction of interrupt handler should be
predictable and short. This is also known as
interrupt latency.

17. •Similarly the time taken between executing the
•Similarly the time taken between executing the
last instruction of the interrupt handler and
last instruction of the interrupt handler and
executing the next task should also be short and
executing the next task should also be short and
predictable. This is also known as interrupt
predictable. This is also known as interrupt
dispatch latency.
dispatch latency.
•Reliable and time bound inter process
•Reliable and time bound inter process
mechanisms should be in place for processes to
mechanisms should be in place for processes to.
communicate with each other in a timely manner.

18. •An RTOS should have support for multitasking
and task preemption. Preemption means to
switch from a currently executing task to a high
priority task ready and waiting to be executed.
•RTOS should be fault tolerant
Some of the most widely used RTOS
are:•LynxOS
•OSE
•QNX
•RTLinux
•VxWorks
•Windows CE

19. Programming languages Used
C is most widely used in RTOS programming
C++ and Ada are the next more popular for large
projects.
Java may also be a choice for some applications