Computer Operating Systems

1. Computer Operating Systems Single-user/Multi-user Operating Systems Dr. E.C. Kulasekere University of Moratuwa

2. Chapter 1 Expectations • Define what an operating system is. • List at least four functions performed by an operating system. • Briefly explain the difference between a general purpose operating system and a dedicated operating system. • classify software according to either business, operating system, utility, education or entertainment categories 2

3. Chapter 1 Expectations (Cont …) • Identify input output devices. • Explain the difference between a single-user operating system and a multi-user operating system. • Identify some of the available operating systems. • Classify common operating systems as single-user or multi-user. 3

4. What is an operating system? • is a collection of system programs that together control the operation of a computer system (?). • The OS is based on particular hardware. 4

5. Abstract view of system components 5

6. What does an operating system do? • The OS controls the way the the Computer Systems functions. • initialize the hardware of the computer system. • provide basic routines for device control • provide for the management, scheduling and interaction of tasks • maintain system integrity and handle errors. • Maintains system clean up functions. 6

7. Where are operating systems found? • The complexity of the OS depends on the type of functions that they provide. • Some OSs are meant for managing networks. • Some are found in petrol pumps. • Some are found in electronic items in homes. • Some are found in cars. • Embedded devices are some examples as well. 7

8. What are General purpose/Dedicated OSs? • Windows operating systems. • Many of the Unix operating systems. • Embedded systems are not GP OSs. • Firmware is also not GP. • The characteristic of a GP OS is its ability to run many software on an application platform. 8

9. Some available operating systems. • MS-DOS • Windows 9x • Windows NT • Windows XP • Windows 200x • Unix – Solaris • Unix - Linux 9

10. Example OS: A security control 10

11. What support utilities are required by an Operating System to perform its tasks? 11

12. What are programs? • A set of instructions for a specific platform? • Byte code? Machine code? • Programming languages (Compilers) • Application software • Special purpose software 12

13. What are input and output devices? • These are devices controlled by the operating system. • Commonly found in most computer systems. • Input devices: Keyboard, mouse tablet, sensors. • Output devices: monitors, printers speakers, actuators. 13

14. What is a single user operating system? • All windows operating systems fall into this category. • In essence, a single-user operating system provides access to the computer system by a single user at a time. • If another user needs to access the computer resources, he/she has to wait until the current user departs. 14

15. What is a multi-user operating system? • It lets more than one user to access the computer system resources at one time. • Access is provided via networks. 15

16. Multi-user ? 16

17. Issues raised by multi-user OSs. • System manages multiple requests to same resource concurrently. • Should avoid deadlocks. • Serial equipment (printers) hooked up to the multi-user OS should be queued. • The OS simulates real time performance by task switching. 17

18. Operating system utilities • The OS is stored in the hard disk. • The part relevant is loaded into RAM at the time of execution. • Some of the utility programs of the OS are • Managing files and documents • Development of programs and software • Communicating with other computer systems. • Managing user requirements for programs, storage space and priority. 18

19. Operating system interfaces • This can be a basic command interpreter (SHELL) like the dos prompt or a Unix command window. • Shell is also called the command line interpreter (CLI). • The interface can be graphical as well. • X-Windows for Unix. • Windows GUI 19

20. Advantages and problems of multi-user OSs • Advantages • Expensive hardware can be shared. • Better utilization of resources and less idle time for each resource. • Problems • As number of users increase the performance degrades. • Some resources such as HD space can be expensive since a lot is needed. • The software is more complicated making it expensive. 20

21. What is a multi-tasking OS? • Ability to run more than one program at a time. • A requirement of a multi-user system. • Simulates real time (Video games) • Increases productivity but also increases coordination complexity. • More resources required. 21

22. What are application software? • Software is another word for program. • Category of software that runs on an operating system platform. • The operating system and nay associated software does not fall into the category of application software. • Enhances the utility value of the operating system. Types: Business, Education, Entertainment, Utility. 22

23. Research Artwork Air control Fishing, coastal data 23

24. Application Software (Cont …) Hair dryer, Washing machine, Kettle, ... 24

25. Summary of Definitions • Whether multiple programs can run on it simultaneously: multi-tasking or Single-tasking if not • Whether it can take advantage of multiple processors: multi-processing • Whether multiple users can run programs on it simultaneously: multi-user 25

26. Summary of definitions (Cont …) • Whether it can reliably prevent application programs from directly accessing hardware devices: protected • Whether it has built-in support for graphics: GUI Based • Whether it has built-in support for networks: Networked 26

27. More classifications • Real-Time Operating System (RTOS): used to control machinery, scientific instruments and industrial systems • Single-User, Single Task: to manage the computer so that one user can effectively do one thing at a time. Palm OS is an example 27

28. More classifications (Cont …) • Single-User, Multi-Tasking: use on their desktop and laptop operating systems today. Examples are windows based OS • Multi-User: allows many different users to take advantage of the computer's resources simultaneously. Example can be UNIX. 28

29. It's important to differentiate here between multi-user operating systems and single-user operating systems that support networking. Windows 2000 and Novell Netware can each support hundreds or thousands of networked users, but the operating systems themselves aren't true multi-user operating systems 29

30. Popular OS classification • Unix: multi-tasking, multi-processing, multi-user, protected, with built-in support for networking but not graphics. • Windows NT: multi-tasking, multi-processing, single-user, protected, with built-in support for networking and graphics. • Windows 95/98: multi-tasking, multi-processing, single-user, unprotected, with built-in support for networking and graphics. 30

31. Popular OS classification (Cont …) • Windows 3.x: single-tasking, single-processing, single-user, unprotected, with built-in support for graphics but not networking. • DOS: single-tasking, single-processing, single-user, unprotected with no built-in support for graphics or networking. • NetWare: multi-tasking, multi-processing, single-user, unprotected, with built-in support for networking but not graphics. 31

32. UNIX: Most popular multi user OS • Solaris, from Sun Microsystems. • AIX, from International Business Machines (IBM). • Digital Unix, from Compaq (which purchased Digital Equipment). • IRIX, from Silicon Graphics (SGI) • HPUX, from Hewlett-Packard. • SCO, from the Santa Cruz Operation. • FreeBSD, maintained by a group of individuals. • OpenBSD, maintained by a group of individuals with a single coordinator. • NetBSD, maintained by a Foundation incorporated in the state of Delaware. • Linux, maintained by a loosely coordinated group of volunteers. 32

33. NT Based: Most popular single user OS • Developed and promoted by Microsoft. • It is multi-tasking • Multi-processor • Network-aware • Used to provide: • Networked file system (NFS) • Printer sharing • Run shared application software. 33

34. Chapter 2 Expectations • list four typical parts (modules) of an operating system. • state three functions performed by a real-time executive. • explain the difference between pre-emptive and co-operative switching. • discuss the relationship between system performance and system overhead. • identify the essential operations that need to be performed in order to switch from one program to another. 34

35. Chapter 2 Expectations (Cont…) • define the terms context switching, system overhead, time-slice, quantum period and scheduling. • distinguish between first-in first-out and round robin scheduling 35

36. What are the various parts of an OS • Real time executive (kernel) is the part of the OS that is responsible for running and coordinating programs. • Modularizing the OS helps coordination of programs in a multi-user environment. Typical modules: • Kernel • Process manager • Scheduler • File manager 36

37. What are the various parts of an OS (Cont …) 37

38. 38

39. Kernel functions • Switching between programs. • Hardware device control and programming. • Memory management. • Process management. • Scheduling. • Inter-process communication. • Processing of exceptions and interrupts. 39

40. How do OSs run more than one program at a time? • Single-user and multi-user OSs both can be multi-tasking. • Single processor or multi processor systems can be multi-tasking. • Simulating multi-tasking using • Co-operative switching. • Preemptive switching 40

41. What is cooperative and preemptive switching? • Co-operative switching means that a task that is currently running will voluntarily give up the processor at some time, allowing other processes to run. • Preemptive switching means that a running task will be interrupted (forced to give up) and the processor given to another waiting process. 41

42. Issues related to task switching • co-operative switching: one process could hang and thus deny execution of other processes, resulting in no work being done.Eg. Win3.1 • Pre-emptive scheduling gives more response to all processes and helps prevent (or reduce the number of occurrences of) the dreaded machine lockup. Eg. Win NT. 42

43. Issues related to task switching (Cont …) • Only 32-bit programs in Windows 95 are pre-emptive switched. 16-bit programs are still co-operatively switched, which means it is still easy for a 16-bit program to lock up a Windows 95 computer. • Advantages gained out weigh the disadvantages associated with switching. 43

44. Chapter 3 Expectations • describe how an operating system is initially loaded. • given a set of characteristics, determine the type of operating system as batch, real-time, time-sharing, interactive or embedded. • state an example of a shell 44

45. How does an OS load itself? • It can be loaded in two ways: • it is already present in ROM (so is permanent, immediately accessible and difficult to update). Eg. Petrol pumps, industrial controllers. Best suited for small and simple OS. • it is loaded from disk to RAM when the computer is turned on. Eg. Win 9x. Easier to update and manipulate. 45

46. What is the bootstrap process? • describes the task of initially loading the operating system from disk into RAM. 46

47. What are the different types of OSs. • Batch • Inter-active • Time-sharing/multi-user • Multi-tasking • Real-time • Multi-processor • Embedded 47

48. What is a shell? • A shell is a program that handles user input and output • It provides routines for handling user input from a keyboard or mouse • It provides routines for displaying information on the terminal screen. • A shell also provides a mechanism to interpret user commands and run additional programs that users request 48

49. Chapter 4 Expectations • define the terms file, cluster, inode, symbolic link • describe a typical structure for the root file system • list four typical entries for a root file entry • explain how free space might be managed • list the file systems supported by Windows 49

50. Chapter 4 Expectations (Cont …) • describe what access or file control permissions are and why they might be needed • explain how the file space may become fragmented, what effect this might have on performance, and how the problem might be corrected 50