1. CHAPTER 2 OPERATING SYSTEM OVERVIEW 1

2. Operating System Operating System Definition A program that controls the execution of application programs and acts as an interface between applications and hardware. 2

3. Layers of Computer System 3

4. Evolution of Operating Systems Historical Timeline 4 GenerationPeriodOperating System Genre First Generation 1945 - 1955 Serial Processing (No Operating System) Second Generation1955 - 1965Simple Batch OS Third Generation1965 - 1980Multiprogramming OS Fourth Generation1980 - presentTime-Sharing OS

5. Second Generation: Simple Batch OS  Simple Batch Systems  Batch jobs together.  Program branches back to monitor when finished.  Jobs read in via punched cards.  Batch systems introduced to reduce wasted time in setting up and running jobs. 5

6. Second Generation: Simple Batch OS (Cont’d)…………X 1. Bring cards to 1401. 2. Read cards to tape offline. 3. Put tape on 7094 which does computing. 4. Put tape on 1401 which prints output offline. 6

7. Second Generation: Simple Batch OS (Cont’d)…………X  Batch Processing: is to batch jobs together.  Uni-Programming: executing one job at a time until finished.  Processor must wait for I/O instruction to complete before proceeding to next instruction. 7

8. Third Generation: Multiprogramming OS……………X  When one job needs to wait for I/O, the processor can switch to the other job 8

9. Third Generation: Multiprogramming OS (Cont’d)………….X 9

10. Fourth Generation: Time-Sharing OS  Uses multiprogramming to handle multiple interactive jobs.  Processor time is shared among multiple users.  In a time-sharing system, multiple users simultaneously access the system through terminals.  Nowadays,  A computer user can listen to audio using RealPlayer while coping some information from the internet using Google Chrome web browser to a MS WORD document.  All of this happens at the same time using time-sharing. 10

11. Services Provided by the Operating System 1) Program development 2) Program execution 3) Access to I/O devices 4) Controlled access to files 5) System Access 6) Error detection and response 7) Accounting 8) Resource Allocation 11

12. Services Provided by the Operating System…………………X 1) Program development - Provide facilities like Editors and debuggers. 2) Program execution – system capability to load a program into memory and to run it. 3) Access to I/O devices - since user programs cannot execute I/O operations directly, the operating system must provide some means to perform I/O. 4) Controlled access to files - program capability to read, write, create, and delete files. 5) System Access - ensuring that all access to system resources is controlled. 12

13. Services Provided by the Operating System (Cont’d)…………X 6) Error detection and response - ensure correct computing by detecting errors in the CPU and memory hardware, in I/O devices, or in user programs.  Example:  Internal and external hardware errors like Memory errors & Device failure  Software errors like Arithmetic overflow & Access forbidden memory locations 7) Accounting - keep track of and record which users use how much and what kinds of computer resources for account billing or for accumulating usage statistics & Monitor performance. 8) Resource Allocation - allocating resources to multiple users or multiple jobs running at the same time. 13

14. System Resources  A resource, or system resource, is any physical or virtual component of limited availability within a computer system.  Major resource types  CPU time  Memory Space  Hard disk space  Network throughput  Electrical power  External Devices  Input/output operations 14 The most significant resources are: CPU Time & Memory Space

15. Objectives of Resource Management  There are three objectives of resource management: 1) Fairness: give equal and fair access to resources. 2) Differential Responsiveness: discriminate among different classes of jobs. 3) Efficiency: maximize throughput, minimize response time, and accommodate as many processes as possible. 15

16. Operating System as a Resource Manager  Operating System manages different resources in order to achieve the formerly-mentioned objectives of resource management.  The major management work as follows: 1) Process Management 2) Main-Memory Management 3) File Management 4) I/O System Management 5) Secondary Management 16

17. (1) Process Management…..X  A process is a program in execution. A process needs certain resources, including CPU time, memory, files, and I/O devices, to accomplish its task.  The operating system is responsible for the following activities in connection with process management. 1) Process creation and deletion. 2) process suspension and resumption. 3) Provision of mechanisms for:  process synchronization  process communication 17

18. (2) Main-Memory Management  Memory is a large array of words or bytes, each with its own address. It is a repository of quickly accessible data shared by the CPU and I/O devices.  Main memory is a volatile storage device. It loses its contents in the case of system failure.  The operating system is responsible for the following activities in connections with memory management: 1) Keep track of which parts of memory are currently being used and by whom. 2) Decide which processes to load when memory space becomes available. 3) Allocate and deallocate memory space as needed. 18

19. (3) File Management  A file is a collection of related information defined by its creator. Commonly, files represent programs (both source and object forms) and data.  The operating system is responsible for the following activities in connections with file management: 1) File creation and deletion. 2) Directory creation and deletion. 3) Support of primitives for manipulating files and directories. 4) Mapping files onto secondary storage. 5) File backup on stable (nonvolatile) storage media. 19

20. (4) I/O System Management….X  The I/O system consists of: 1) A buffer-caching system 2) A general device-driver interface 3) Drivers for specific hardware devices 20

21. (5) Secondary-Storage Management  Since main memory (primary storage) is volatile and too small to accommodate all data and programs permanently, the computer system must provide secondary storage to back up main memory.  Most modern computer systems use disks as the principle on-line storage medium, for both programs and data.  The operating system is responsible for the following activities in connection with disk management: 1) Free space management 2) Storage allocation 3) Disk scheduling 21

22. Kernel  Portion of operating system that is in main memory.  Contains most frequently used functions.  Also called the nucleus. 22

23. Process  A program in execution.  An instance of a program running on a computer.  The entity that can be assigned to and executed on a processor.  A process consists of three components: 1) An executable program. 2) Associated data needed by the program. 3) Execution context of the program.  All information the operating system needs to manage the process. 23