Introduction To Computing Lecture # 5

1. Introduction To Computing Lecture # 5 By Omer Iqbal Email Omer.iqbal@hotmail.com

2. Introduction • What is an operating system? • Early Operating Systems • Simple Batch Systems • Multiprogrammed Batch Systems • Time-sharing Systems • Personal Computer Systems • Parallel and Distributed Systems • Real-time Systems Introduction to Computing 2009

3. WHAT IS AN OPERATING SYSTEM? • An interface between users and hardware - an environment "architecture” • Allows convenient usage; hides the tedious stuff • Allows efficient usage; parallel activity, avoids wasted cycles • Provides information protection • Gives each user a slice of the resources • Acts as a control program. Introduction to Computing 2009

4. operating system operating system operating system operating system Introduction to Computing 2009

5. Operating System • The most important program that runs on a computer. Every general-purpose computer must have an operating system to run other programs. • Operating systems perform basic tasks, such as recognizing input from the keyboard, sending output to the display screen, keeping track of files and directories on the disk, and controlling peripheral devices such as disk drives and printers. • For large systems, the operating system has even greater responsibilities and powers. It is like a traffic cop -- it makes sure that different programs and users running at the same time do not interfere with each other. The operating system is also responsible for security, ensuring that unauthorized users do not access the system. Introduction to Computing 2009

6. Goals of an Operating System • Simplify the execution of user programs and make solving user problems easier. • Use computer hardware efficiently. • Allow sharing of hardware and software resources. • Make application software portable and versatile. • Provide isolation, security and protection among user programs. • Improve overall system reliability • error confinement, fault tolerance, reconfiguration. Introduction to Computing 2009

7. Why should I study Operating Systems? • Need to understand interaction between the hardware and applications • New applications, new hardware.. • Need to understand basic principles in the design of computer systems • efficient resource management, security, flexibility • Increasing need for specialized operating systems • e.g. embedded operating systems for devices - cell phones, sensors and controllers • real-time operating systems - aircraft control, multimedia services Introduction to Computing 2009

8. Operating System Objectives • Convenience • Makes the computer more convenient to use • Efficiency • Allows computer system resources to be used in an efficient manner • Ability to evolve • Permit effective development, testing, and introduction of new system functions without interfering with service Introduction to Computing 2009

9. Classification of OS • Operating systems can be classified as follows: • multi-user: Allows two or more users to run programs at the same time. Some operating systems permit hundreds or even thousands of concurrent users. • multiprocessing:Supports running a program on more than one CPU. • multitasking: Allows more than one program to run concurrently. • multithreading: Allows different parts of a single program to run concurrently. • real time: Responds to input instantly. General-purpose operating systems, such as DOS and UNIX, are not real-time. Introduction to Computing 2009

10. Layers of Computer System Introduction to Computing 2009

11. Services Provided by the Operating System • Program development • Editors and debuggers • Program execution • Access to I/O devices • Controlled access to files • System access Introduction to Computing 2009

12. Services Provided by the Operating System • Error detection and response • Internal and external hardware errors • Memory error • Device failure • Software errors • Arithmetic overflow • Access forbidden memory locations • Operating system cannot grant request of application Introduction to Computing 2009

13. Services Provided by the Operating System • Accounting • Collect usage statistics • Monitor performance • Used to anticipate future enhancements • Used for billing purposes Introduction to Computing 2009

14. Operating System • Responsible for managing resources • Functions same way as ordinary computer software • It is program that is executed • Operating system relinquishes control of the processor Introduction to Computing 2009

15. Introduction to Computing 2009

16. Kernel • Portion of operating system that is in main memory • Contains most frequently used functions • Also called the nucleus Introduction to Computing 2009