Operating system 1Chapter One- Introduction(0) (1).pptx

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1. Introduction Chapter 1 1 Operating System

2. OUTLINE Definition of operating system Reasons for studying OS OS components OS functions Type of systems Batch Systems Time-sharing system Single User Interactive system Parallel system Distributed system Real-time system Single-tasking system Multi-tasking system Interrupts OS services System call System structure 2

3. What is an Operating System? • A program that acts as an intermediary between a user of a computer and the computer hardware. • Operating system goals: Execute user programs and make solving user problems easier . Make the computer system convenient to use. • Use the computer hardware in an efficient manner. 3

4. Indicate Some Reasons for Studying Operating Systems Understand how computers work under the hood To learn how to manage complexity through appropriate abstractions To learn about system design. Because OSs are everywhere! 4

5. Computer System Components 1. Hardware – provides basic computing resources (CPU, memory, I/O devices). 2.Operating system – controls and coordinates the use of the hardware among the various application programs for the various users. 3. Applications programs – define the ways in which the system resources are used to solve the computing problems of the users (compilers, database systems, video games, business programs). 4. Users (people, machines, other computers). 5

6. Abstract View of System Components 6

7. Operating System Definitions Software between applications and hardware Resource allocator – manages and allocates resources . Resource Manager Give resources to applications Take resources from applications Protection and Security Control program – controls the execution of user programs and operations of I/O devices . Kernel – the one program running at all times (all else being application programs). 7

8. Operating System Functions Process Management Creating and destroying the user and system processes. Allocating hardware resources among the processes. Controlling the progress of processes. Providing mechanisms for process communications. Memory Management Keep track of each location of memory, i.e. each memory location is either free or allocated. De-allocation technique policy for memory 8

9. Operating System Functions (Cont.) File Management Creating and deleting of files and directories. Mapping files onto secondary storage. Backing up files on stable storage media. Transmission of file elements between main and secondary storage I/O System Management It includes buffering, caching and spooling. A general device driver interface. Drivers for specific hardware devices 9

10. Types of Systems Batch system submit large number of jobs at one time system decides what to run and when Time Sharing system multiple users connected to single machine few processors, many terminals Single User Interactive system one user, one machine traditional personal computer

11. Types of Systems Parallel system traditional multiprocessor system higher throughput and better fault tolerance Distributed system networked computers Real Time system very strict response time requirements hardware or software

12. Single Tasking System Only one program can perform at a time Simple to implement only one process attempting to use resources Few security risks Poor utilization of the CPU and other resources Example: MS-DOS

13. Multitasking System Very complex Serious security issues how to protect one program from another sharing the same memory Much higher utilization of system resources Example: Unix, Windows NT

14. Interrupts Interrupt is an event external to the currently executing program that causes a change in the normal flow of instruction execution; usually generated by hardware devices external to the CPU. Interrupts are signals sent to the CPU by external devices, normally I/O devices. They tell the CPU to stop its current activities and execute the appropriate part of the operating system . The occurrence of an event is usually signaled by an interrupt either from the hardware or the software. Interrupts are important because they give the user better control over the computer. Without interrupts, a user may have to wait for a given application to have a higher priority over the CPU to be ran. This ensures that the CPU will deal with the process immediately. 14

15. Interrupts ( Cont.) Why Interrupts? People like connecting devices A computer is much more than the CPU Keyboard , mouse, screen, disk drives, Scanner , printer, sound card, camera, etc. These devices occasionally need CPU service But we can’t predict when External events typically occur on a macroscopic timescale we want to keep the CPU busy between events Need a way for CPU to find out devices need attention 15

16. Interrupts ( Cont.) Possible Solution: Polling CPU periodically checks each device to see if it needs service × takes CPU time even when no requests pending × overhead may be reduced at expense of response time can be efficient if events arrive rapidly “ Polling is like picking up your phone every few seconds to see if you have a call. …” 16

17. Interrupts ( Cont.) Alternative: Interrupts Give each device a wire (interrupt line) that it can use to signal the processor When interrupt signaled, processor executes a routine called an interrupt handler to deal with the interrupt No overhead when no requests pending 17

18. Interrupts ( Cont.) Polling vs. Interrupts Polling is like picking up your phone every few seconds to see if you have a call. Interrupts are like waiting for the phone to ring . Interrupts win if processor has other work to do and event response time is not critical Polling can be better if processor has to respond to an event timely. May be used in device controller that contains dedicated secondary processor 18

19. Interrupts ( Cont.) Types of Interrupts Hardware interrupts are generated by hardware devices to signal that they need some attention from the OS. They may have just received some data (e.g., keystrokes on the keyboard or a data on the Ethernet card); or they have just completed a task which the operating system previous requested, such as transferring data between the hard drive and memory. Software interrupts Used to transfer control to the operating system Program generated interrupts are a means for user programs to call a function of the operating system Software may trigger an interrupt by executing a special operation called system call Traps(Exceptions) Exception within a program When the hardware detects that the program is doing something wrong, it will usually generate an interrupt. 19

20. Operating System Services An operating system provides an environment for the execution of programs by providing services needed by those programs. Program execution – system capability to load a program into memory and to run it. I/O operations – since user programs cannot execute I/O operations directly, the operating system must provide some means to perform I/O. File-system manipulation – program capability to read, write, create , and delete files. Communications – exchange of information between processes executing either on the same computer or on different systems tied together by a network. Implemented via shared memory or message passing . Error detection – ensure correct computing by detecting errors in the CPU and memory hardware, in I/O devices, or in user programs . 20

21. Operating System Services ( Cont.) Additional functions exist not for helping the user, but rather for ensuring efficient system operations. Resource allocation – allocating resources to multiple users or multiple jobs running at the same time. 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. Protection – ensuring that all access to system resources is controlled . 21

22. System Calls System calls are routines run by the OS on behalf of the user the method used by a process to request action by the operating system . Applications cannot perform privileged operations themselves Must request OS to do so on their behalf by issuing system calls If a process is running a user program in user mode and needs a system service, such as reading data from a file, it has to execute a trap instruction to transfer control to the operating system. The operating system then figures out what the calling process wants by inspecting the parameters. Then it carries out the system call and returns control to the instruction following the system call . 22

23. System Calls (Cont.) System calls can be grouped roughly into five major categories : Process control end, abort load, execute create process, terminate process get process attributes, set process attributes wait for time wait event, signal event allocate and free memory File management create file, delete file open, close read, write, reposition get file attributes, set file attributes 23

24. System Calls (Cont.) Device management request device, release device read, write, reposition get device attributes, set device attributes logically attach or detach devices Information maintenance get time or date, set time or date get system data, set system data get process, file, or device attributes set process, file, or device attributes 24

25. System Calls (Cont.) Communications create, delete communication connection send, receive messages transfer status information attach or detach remote devices 25

26. System Structure A system as large and complex as a modern operating system must be engineered carefully if it is to function properly and be modified easily. The essence of operating system structure is to manage the complexity of the software. Operating system structure refers to the internal organization of the software . 26