1. Introduction to Operating System and Operating System Components
Lecture 1
Introduction to Operating System and Operating System Components

2. Lecture Highlights What is an operating system
Definition
Purpose and Goals
Operating system as part of a computer system
Operating system components
A closer look at some critical operating system functions
Operating system classification

3. Operating System Definition
An operating system is simply a system application which manages user applications and their interaction with the system hardware.
An operating is a program that acts as an intermediary between a user of a computer and the computer hardware.
Operating system is a resource allocator. Much of the operating system theory concentrates on optimal use of computing resources.

4. Purpose and Goals of an operating system
The purpose of an operating system is to provide an environment in which a user can execute programs
The two goals:
Make the computer system convenient to use
Use the computer hardware in an efficient manner

5. Goals of an operating system Convenience vs. Efficiency
Convenience for user: Operating systems exist because they are supposed to make it easier to compute than without one. This view is particularly clear when you look at operating systems for small personal computers.
Efficient operation: This goal is particularly important for large, shared multiuser systems. These systems are typically expensive, so it is desirable to make them as efficient as possible.
These two goals, convenience and efficiency, are sometimes contradictory. In the past, efficiency considerations were often more important than convenience. Thus, much of the operating-system theory concentrates on optimal use of computing resources.

6. Operating system as part of a computer system
The four components of a computer system:
Hardware
Operating system
Application programs
Users

7. Four components of a computer system - Hardware
It is comprised of the CPU, memory, and input/output devices.
It provides the basic computing resources.

8. Four components of a computer system – Application Programs
They define the ways in which the hardware resources are used to solve the computing problems of the users.
There are many different application programs e.g. compilers, database systems, games, business programs, etc.

9. Four components of a computer system – Operating System
The operating system controls and coordinates the use of the hardware among the various application programs for the various users.
It provides an environment within which other programs can do useful work.
It is a control program that controls the execution of user programs to prevent errors and improper use of the computer.

10. Operating System Components
Interface
Process management
Memory management
I/O system management
File Management
Security / Protection System
Networking
Command-Interpreter System

11. Operating System Components Interface
The interface can be a fancy windows based or a command line interpreter. The issue is usually efficiency versus convenience. Various operating systems try to strike a balance between the two depending on specific needs.

12. Operating System Components Process Management
This component is related to the concept of time multiplexing for the CPU. It aims at making the process of switching between two programs transparent to the user.

13. Operating System Components Memory Management
This component is tied with the concept of space multiplexing.
It entails both main memory management as well as secondary management.

14. Operating System Components I/O System Management
The operating system hides the peculiarities of specific hardware devices from the user by providing drivers for specific hardware devices on one hand and a general device-driver interface on the other hand.

15. Operating System Components File Management
The operating system provides a uniform logical view of information storage.
It maps files onto physical media, and accesses these files via the storage devices.

16. Operating System Components Security/Protection Management
In multi-user and multitasking systems, the various processes must be protected from one another’s activities. For that purpose, mechanisms are provided to ensure that the files, memory segments, CPU, and other resources can be operated on by only those processes that have gained proper authorization from the operating system.

17. Operating System Components Networking
Operating system usually generalizes network access as a form of file access, with the details of networking being contained in the network interface’s device driver.

18. Operating System Components Command Interpreter System
Command interpreter provides the interface between the user and the operating system.
The command statements deal with process creating and management, I/O handling, memory management, file-system access, protection, and networking.

19. Operating System Components Command Interpreter System (..contd)
Operating systems are frequently differentiated in the area of command interpretation, with a user-friendly interpreter making the system more agreeable to some users.An example of a user-friendly interface is the Macintosh interpreter, a window and menu system that is almost exclusively mouse based. Depending on the cursor location, clicking the mouse’s button can invoke a program, select a file or directory, or pull down a menu containing commands.

20. Operating System Components Command Interpreter System (..contd)
More powerful, complex, and difficult-to-learn interpreters are appreciated by other, more sophisticated users. On these interpreters, commands are typed on a keyboard and displayed on a screen or printing terminal, with the enter key signaling that a command is complete and is ready to be executed. The UNIX shells run in this mode.

21. Some Critical Operating System Functions – A Closer Look
Process Management
Memory Management
Input/Output Management
General Support Functions

22. Process Management A Closer Look
Creation and Termination of processes
Scheduling, Dispatching and Switching processes
Synchronization, Communication and Deadlock Avoidance

23. Process Management A Closer Look
Creation and Termination of processes
A process is a pre-written set of ordered instructions which when executed causes the computer to behave in a manner determined by the code
A process is a program in execution
New process are spawned either by a user or by other processes.

24. Process Management A Closer Look
Scheduling, Dispatching and Switching processes
An operating system must select processes for execution in some fashion.
CPU scheduling deals with the problem of deciding which of the processes in the ready queue is to be allocated the CPU.
The selection process is carried out by an appropriate scheduling algorithm.

25. Process Management A Closer Look
Synchronization, Communication and Deadlock Avoidance
Concurrent access to shared data can result in data inconsistency.
To ensure orderly execution of processes , the operating system provides mechanisms for job synchronization and communication.
A deadlock state is a state of indefinite wait by one or more processes for an event that can be triggered only by one of the waiting processes.
Operating system also provides mechanisms to ensure that jobs do not get stuck in a deadlock, forever waiting for each other.

26. Memory Management A Closer Look
Memory Allocation
Swapping
Page and Segment Management

27. Memory Management A Closer Look
Memory management primarily deals with space multiplexing.
All the processes need to be scheduled in such a way that all the users get the illusion that their processes reside on the RAM.
The job of the memory manager:
keep track of which parts of memory are in use and which parts are not in use
to allocate memory to processes when they need it and deallocate it when they are done
to manage swapping between main memory and disk when main memory is not big enough to hold all the processes.

28. Input/Output Management A Closer Look
Buffer Management
Device Allocation

29. Input/Output Management A Closer Look
One of the purposes of an operating system is to hide the peculiarities of specific hardware devices from the user. For example, in UNIX, the peculiarities of I/O devices are hidden from the bulk of the operating system itself by the I/O system. The I/O system consists of:
A buffer-caching system
A general device-driver interface
Drivers for specific hardware devices
Only the device driver knows the peculiarities of the specific device to which it is assigned.

30. General Support Functions A Closer Look
Interrupt Handling
Accounting
Monitoring

31. General Support Functions A Closer Look
Interrupt Handling
The occurrence of an event is usually signaled by an interrupt from either the hardware or the software.
There are many different types of events that may trigger an interrupt, for example, the completion of I/O operation, division by zero, invalid memory access, and a request for some operating system service.
For each such interrupt, a service routine is provided that is responsible for dealing with the interrupt.

32. General Support Functions A Closer Look
Accounting
Accounting entails keeping track of which users use how much and what kinds of computing resources.
This record keeping may be for billing purposes or simply for accumulating usage statistics.
Usage statistics may be a valuable tool for researchers who wish to reconfigure the system to improve computing services.

33. Operating System Classification
Operating system can be classified as follows:
Multi-user
Multiprocessing
Multitasking
Multithreading
Real time

34. Multi-user operating system
A multi-user operating system allows two or more users to run programs at the same time. Some operating systems permit hundreds or even thousands of concurrent users.

35. Multiprocessing Operating System
A multiprocessing operating system supports running a program on more than one CPU.

36. Multitasking Operating System
A multitasking operating system allows more than one program to run concurrently.

37. Multithreading Operating System
A multithreading operating system allows different parts of a single program to run concurrently.

38. Real time operating system
A real time operating system responds to input instantly. General purpose operating systems, such as DOS and UNIX, are not real time.

39. Lecture Summary What is an operating system
Definition
Purpose and Goals
Operating system as part of a computer system
Operating system components
A closer look at some critical operating system functions
Operating system classification

40. Preview of next lecture
The following topics shall be covered in the next lecture:
Process Concepts
Performance Measures
Evaluation Techniques