1. OPERATING SYSTEMS Software in the Background
Chapter 2

2. Objectives Describe the functions of an Operating System
Explain the basics of a personal computer operating system
Describe the advantages of a graphical operating system
Differentiate among different versions of Microsoft Windows
Explain the need for network operating systems
Describe the methods of resource allocation on large computers
Be able to describe the differences among multiprocessing, multiprogramming, and timesharing
Explain the principles of memory management
List several functions typically performed by utility programs

3. Contents Operating System: Hidden Software Systems Software
Functions of OS
Types of OS
MS-DOS
Microsoft Windows
Mac OS
UNIX
LINUX
Network Operating System NOS
Resource Allocation
Utility Programs

4. Operating System Hidden Software
Definition – provides access to all resources
Kernel
Manages the operating system
Memory resident
Loads set of programs that lies between applications software and the hardware
Fundamental software that controls non-resident portions of the OS as needed
Booting – Loads the kernel into memory

5. Systems Software Definition: Components
All programs related to coordinating computer operations
Components
Operating System
Utility programs
Program language translators

6. Functions of OS Manage the computer’s resources
CPU
Memory
Disk drives
Printers
Establish a user interface
Execute and provide services for applications software
Carries out all input and output operation

7. User Interface
Facilitates communication between the user and the operating system
Two forms
Command line
Text-based
Key commands
Examples: MS-DOS, Unix
Graphical user interface (GUI)
Visual images
Menus
Examples: Windows, Mac OS, Linux

8. Platform Definition: Wintel
Computer hardware and operating system software that dictate what other software can run
Wintel
Intel-based PC running Microsoft Windows

9. OS is Hidden
User interested in application software to make the PC useful
Application software is platform specific
User must be aware of the type of OS
User should be aware of the functions of OS

10. Network Operating System (NOS)
Types of OS
Command line
Single user PC
Network Operating System (NOS)

11. MS-DOS Command-line interface
Prompt – system is waiting for you to do something
Key a command
Not user-friendly

12. Microsoft Windows Graphical user interface Eases access to the OS
Most new computers come with Windows already installed

13. GUI On-screen pictures Fast Easy Intuitive Icons Menus
Pull down
Pop up
Click to activate a command or function
Fast
Easy
Intuitive

14. Early Days of Windows Operating environment for MS-DOS
Shell – layer added between users and DOS

15. Windows Today Home/consumer market Corporate market Windows XP
Windows Millennium Edition (ME)
Corporate market
Windows NT
Windows 2000
Windows XP
Pocket computers and Internet appliances
Windows CE

16. Windows 95 and 98 Self-contained OS DOS commands still available
Start programs by
Start button
Double clicking the icon
Task bar permits movement between open programs
Long file names up to 255 characters
Plug and play
Object linking and embedding (OLE)

17. Windows 98 Additions Internet / intranet browsing
Support for DVD and additional multimedia components
Support for large hard drives
TV viewer and broadcast ability
Wizards

18. Improved Windows Features
Backup
Interfaces with other software
Networking features
Security
Dr. Watson

19. Windows
Helps reduce the cost of owning and maintaining a PC

20. Windows ME Millennium Edition
Multimedia support -- Windows Media Player 7
Jukebox
Record music CDs as digital files
Windows Movie Maker
Basic video editing
Windows Image Acquisition
Scanner and digital camera

21. Windows ME Millennium Edition
Reliability Features
System File Protection
AutoUpdate
System Restore
Help Center
Home Network Support
Wizard for connecting multiple computers and peripherals
Multiple users can share a single Internet connection

22. Windows NT New Technology
Engineered for stability
Strong security
Versions
NT Workstation
NT Server
Drawbacks
Lacks support for older Windows and MS-DOS software and hardware
Complex to learn and use
Requires more memory and processing power

23. Windows 2000 Stability features Security features
Uses simple approach to hardware setup from Windows 98
Versions
Windows 2000 Professional for individual users
Windows 2000 for network servers
Was intended for both the corporate and home use, replacing Win NT and Win 98

24. Windows 2000 Complex Heavy demand for computer resources
Improvements over windows NT
Maintains user preferences
Self-healing applications software
Supports Windows 98 file structure
Uses plug and play
Provides improved support for laptops

25. Windows XP Extends Windows ME and provides a more stable environment
Two categories
Network server
3 versions based upon network complexity
Desktop computer
2 versions
Professional Client
Personal Client

26. Windows CE Consumer Electronics
Where used
Embedded systems
Industrial controllers
Robots
Office equipment
Cameras
Telephones
Home entertainment devices
Automobile navigation systems
Pocket PC
Internet appliance market

27. Windows CE Consumer Electronics
Subset of Windows
Less memory
Smaller screens
Little or no file storage
Provides Internet connectivity

28. Accessibility Options
Seeing
Hearing
Touching

29. Mac OS First commercially successful GUI (1984)
Served as a model to other GUI systems

30. UNIX Supports Character-based system Command-line interface
Multi-user
Time-sharing
Character-based system
Command-line interface
Runs on various processors and many types of computers
Primary OS used on Internet servers

31. LINUX UNIX-like OS Open-source software PC Setup Download it free
Make changes
Distribute copies
Restriction – any changes must be freely available to the public
PC Setup
PC comes with Windows installed
Install LINUX in a dual-boot configuration

32. LINUX Advantages over Windows Disadvantage Extremely stable
Internet support
Reinstallation is simpler
Disadvantage
Scarcity of applications

33. Network Operating System NOS
Designed to permit computers on a network to share resources
Examples
Windows 2000 Server
Novell Net Ware
Provides
Data security
Troubleshooting
Administrative control

34. NOS Functions Split between client and server computers Server Client
File management
Client
Requests to the server
Messaging
Has own local OS
Makes the resources appear as if they are local to the client’s computer

35. Large Computers Used by many people at once
OS works “behind the scenes” so users can share
OS must control
Who gets access to resources
What keeps the programs from different users from getting mixed up with one another

36. Resource Allocation
Resource – hardware or software that is needed to complete a task
Resource Allocation – assigning computer resources to certain programs
Resource De-allocation – releasing resources when a task is complete

37. Allocating the CPU One CPU More than one CPU Multiprogramming
Event-driven
Timesharing
More than one CPU
Multiprocessing – multiple CPUs can run several programs simultaneously

38. Multiprogramming One CPU Concurrent execution of two or more processes
Several processes open at once
Only one process can receive the attention of the CPU at any given moment
Effective because CPU speeds are many times faster than input/output speeds

39. Event-driven Multiprogramming
One program receives the attention of the CPU
Its processing will be interrupted based upon events in the program
When processing needs to be temporarily suspended, an interrupt is generated
This is a signal to the operating system to evaluate the cause of the interrupt and determine who should now have CPU time

40. Event-driven Multiprogramming Example
Two programs are running – Payroll and Inventory Management
Payroll needs to read an employee record
Payroll generates an interrupt
Normal processing is temporarily suspended
The CPU looks at the interrupt and initiates the read operation
While waiting for the read to complete, the CPU begins processing the Inventory Management program

41. Event-driven Multiprogramming Example
When the read operation is complete, another interrupt is generated
Normal processing is temporarily suspended
The CPU looks at the interrupt and determines its cause
The CPU will either continue processing the Inventory Management program or return to the Payroll program depending upon their priority

42. Time-sharing Multiprogramming
One program receives the attention of the CPU
A small fraction of CPU time is allocated to the program
The time slice ends
The CPU begins processing a different program
Response time can vary based upon the number of users on the system

43. Sharing Memory Program must be in memory to be executed Problems
Programs compete for space
May have a very large program
Memory space for each program must not overlap

44. Memory Management
The process of providing separate memory space to programs
Memory Protection keeps one program from interfering with another

45. Memory Management Methods
Partitions or regions
Foreground and background
Virtual storage (virtual memory)

46. Partitions or Regions Divide memory into sections
The partition must accommodate the largest possible program
Problem
May cause wasted memory space

47. Foreground and Background
Programs are placed in either Foreground or Background
Programs in Foreground have priority for CPU time
While performing read / write operations for the Foreground program, the CPU gives time to a program in Background
Programs are placed in a holding queue while waiting to run

48. Virtual Storage Virtual Memory
Uses concept of Paging
Divide the program into equal-size pieces (pages)
Store each piece in equal-size memory spaces (page frames)
Typical size is 2KB or 4KB
Create an index to each page and store in a Page Table

49. Virtual Storage Virtual Memory
Paging Process
A portion of the program is placed in memory
The remainder is on disk
Sections on disk will be brought into memory as needed (one page at a time)

50. Virtual Storage Virtual Memory
Problem -- Thrashing
Too large a portion of CPU time is spent locating the correct page and bringing it into memory
Solution
Run fewer programs concurrently
Add memory

51. Memory Protection Keeps one program from straying into another
Confines each program to certain defined limits in memory
Why needed
Possible for one program to destroy or modify another by transferring to the wrong memory location
May cause destruction of data
Action if assigned memory space is violated
Termination of executing program

52. Sharing Storage Several users need to access the same disk pack
One wants to write
Another wants to read
OS keeps track of the I/O requests
OS processes I/O requests in order received

53. Sharing Printing Resources
Print resources are shared between active programs
Printouts are generated in pieces as the CPU gives each concurrent program some time
Problem
The current program may generate a few print lines
The CPU moves to the next program
The second program may generate a few print lines, etc.

54. Sharing Printing Resources
Result
Printout is worthless as it contains a few lines from several programs
Solution – Spooling
Each program thinks it is writing to the printer
The program actually writes to the hard disk
When the program is complete, the file on the hard disk is sent to the printer

55. Additional Printing Problem
Printers are slow compared to the CPU speed
Solution
The CPU writing to the disk
The program completes quicker

56. Utility Programs Come with System Software Handle special needs
Perform secondary chores
Do not need to be memory resident

57. Functions of Utility programs
File manager – provide access to lists of stored files
Backup and Restore – make duplicate copies of important files and return the copy to the hard drive if needed
File compression – reduces the amount of disk space required by a file
Disk defragmenter – reorganize files so they are stored contiguously on disk providing for faster access
Device drivers – convert operating system instructions into commands that are known to a specific device