1. Tonga Institute of Higher Education IT 141
Lecture 5: Operating System

2. Operating System (OS)
Type of software that acts as the master controller for all activities that take place within a computer system
E.g. – Microsoft Windows, Mac OS, Linux, DOS, UNIX, Solaris, and BeOS
Window software are designed to run on computers that have Microsoft Windows (MSWord, Excel etc.) Mac Software is designed to run under Mac OS. Linux software is designed to run under Linux operating system

3. What does an OS do? Device drivers tell hardware
You tell the computer what to do using application software
Application software tells the OS what to do
Operating system tells device drivers
Device drivers tell hardware
Hardware does the work
You issue print while using app software (Word) – Word processing app signals OS that document must be sent to the printer – OS communicates the doc data to the device driver for printer – device driver controls printer as it prints the document

4. What does an OS do?

5. OS Tasks Manage processor resources Manage memory
Keep track of storage resources
Ensure that input and output proceed in an orderly manner
Establish basic elements of the user interface
The operating system interacts with application software, device drivers, and hardware to manage a computer’s resources. In the context of a computer system, the term resource refers to any component that is required to do work. E.g. processor is a resource. RAM, storage space, and peripherals are also resources.

6. How OS manage processor resources
Processes – activities
Processes compete for your computer’s microprocessor’s attention
OS must ensure that each process receives its share of microprocessor cycles

7. OS handling so many processes
Can be managed by
Multitasking
Multithreading
Multiprocessing
Multitasking provides process and memory management services that allow two or more tasks, jobs, or programs to run simultaneously. Most of today’s operating systems offer multitasking.
Within a single program, multithreading allows multiple parts, or threads to run simultaneously. E.g. one thread for a spreadsheet program might be waiting for input from the user while other threads perform a long calculation in the background. Multithreading can speed up a performance on single or multiple processor computers.
Many new computers include multi-core processors or multiple processors. An OS multiprocessing capability supports a division of labour among all the processing units.

8. OS managing memory
Microprocessor works with data and executes instructions stored in RAM
OS divide up specific areas of memory for each program
Prevents a memory leak.
Use Ctrl+Alt+Del key to close corrupted programs

9. OS keeping track of storage resources
Acts as a filing clerk
Remembers names and locations of files
Keeps track of empty spaces
Filing clerk that stores and retrieves files from your disks or CDs

10. OS and peripheral devices
OS communicates with device driver software so that data travel smoothly between computer and peripheral devices
OS makes sure that input and output continue in an orderly manner
Buffers collect and hold data when busy
Buffer – part of memory that holds data waiting to be transferred from one device to another
Keyboard buffer – you never miss a stroke no matter how fast you type

11. Different OS needed for different computing tasks
Single-user OS – deal with one set of input devices. E.g. DOS
Multiuser OS – allows a single, centralized computer to deal with simultaneous input, output, and processing requests from many users. E.g. – IBM’s z/OS
Server OS – provides tools for managing distributed works, servers, and Web hosting sites. E.g. – Mac OS X Server, Windows Server 2008
Desktop OS – designed for a PC. E.g. – Microsoft Windows or Mac OS

12. Interacting directly with OS
When you start your computer
Manage files (Windows Explorer): allows you to view, move, copy, rename or delete
Get help
Customize interface: help you customize your screen display and work environment
Configure equipment: access and utilities to help set up and configure computer’s hardware and peripheral devices

13. User Interfaces
Definition: mixture of hardware and software that helps people and computers communicate with each other
OS defines the look and feel of compatible software
Know what
Icon, desktop, window, taskbar, toolbar, ribbon, menu, submenu, tab, etc.
OS defines the look and feel of compatible software
Graphical user interface (GUI): point and click.
Icon – small picture that represents a program, file, or hardware
Window – rectangular work area that hold a program, data, or controls

14. Windows, Mac OS, and Linux similar?
They differ in their visual design

15. Boot Process Digital devices – OS is stored in ROM
Larger devices – OS is quite large, stored in hard disk
Boot process – operating system kernel loaded into RAM
Kernel provides key OS services such as memory management and file access.
Kernel stays in RAM all the time your comp is on.
Other OS parts are only loaded when needed

16. Boot Process
Steps of events that happen between the time you turn on the comp, and the time it is ready for you to issue commands
Bootstrap program is built into special ROM chip in the computer’s system unit. When it receives power, it starts the boot processing by executing the bootstrap program.

17. Boot process major events
Power up
Start boot program
Power-on self-test
Identify peripheral devices
Load operating system
Check configuration and customization

18. OS in hard disks
Because RAM is volatile, we can’t store OS in hard disks. ROM and EEPROM are non-volatile, and can still store data even when the power is off, but too small for OS.
During booting, OS is transferred into RAM

19. 6 major events during the boot process
Power up
Start boot program
power-on self test
Identify peripheral devices
Load OS
Check configuration and customization
1. Power light is on, power distributed to the comp circuitry. 2. microprocessor starts executing bootstrap prog stored in ROM. 3. comp does diagnostic test of several very important system parts. 4. OS identifies peripherals and their settings. 5. OS copied from HD to RAM. 6. microprocessor reads config data and does any specially made startup techniques specified by the user.

20. Why OS is stored in HD not RAM
Because RAM is volatile
EEPROM and ROM are non volatile but their storage capacity are not big enough
OS is transferred to RAM for quick access

21. Bootstrap summary

22. Microsoft Windows OS
Microsoft Windows (Windows 1.0, Windows 2.0……Windows 2008)
Adv: variety of hardware platforms, user community, gives excellent support in the form of built-in drivers and plug and play funcitonality
Disadv: reliability and security
There are different Microsoft windows for different computer categories
Different platforms – desktop, notebook, ultr-mobile PC, tablet computer, handwriting recognition for PDAs and tablet comps with touch screens
User community – vast amount of documentation, including tutorials and troubleshooting guides
Many of the fastest graphic cards are offered exclusively for the Windows platform
Disad: compared to other OS in speed

23. Microsoft Windows versions
Personal computers
LAN, Internet, and Web Servers
PDAs, Mobile Phones, and Non-personal Computer Devices
Windows Vista Starter, Windows Vista Home Basic, Windows Vista Home Premium
Windows Server 2008
Windows Server 2003
Windows 2000 Server
Windows Mobile OS
Windows Embedded OS
Windows XP Embedded

24. MAC OS
Macintosh OS
For Apple Computer’s Macintosh line of computer systems
Classic Mac OS, System 6, System 7/Mac OS,…. Mac OS X 10.5 (Leopard)
Adv: easy to use, reliable, and secure. Offers strong backward compatibility, dual boot options, and good virtual machine platform
Disadv: limited selection of software
Backward compatibility – ability to work with products designed for prior-generation hardware and software. E.g. suppose you have a computer and lots of great software, but you purchase a faster machine with an upgraded OS. If the OS is backward compatibility with the OS on your old computer, you can use all of your old applications.
Dual boot – can switch between Mac OS X and Windows. When booting, you can select either Mac OS X or Windows. To change operating systems, you have to reboot.
Virtual machine – technology that allow you to use one computer to copy the hardware and software of another

25. UNIX and LINUX OS
Linux developed based on a UNIX derivative called MINX
Linux adv: distributed with source code for everyone to use.
Disadv: mostly for technical users
UNIX available for mainframes and microcomputers
Linux is designed for microcomputers rather than mainframes.

26. DOS (Disk Operating System)
First OS and old, developed by Microsoft
Command-line user interface

27. Handheld Operating System
Palm OS, Windows Mobile OS, iPhone OS X, Symbian OS
OS for handheld and desktop gives similar services but handheld devices are simpler therefore their OS are simpler and smaller. The OS can be stored in ROM.

28. File Basics
File – named collection of data that exists on a storage medium
File-naming conventions. Each OS has a unique set of rules. Max length for naming files is 255 characters.
File name extension – optional file identifier separated from the main file by a period (E.g. pain.exe, .dat – document, .doc – word processing

29. File Basics
Reserved words – words used as commands or special identifiers that you CANNOT USE as a file name (e.g. – Nul, Aux, Com1, Com2, Con, Lpt1, Lpt 2)
Some OS are case sensitive. Upper and Lowercase letters.

30. File Directories and folders
You can choose a file’s location
Disk partition – section of a hard disk drive that is treated as a separate storage unit. Can be assigned drive letters. Partition C, or D. It is NOT like folders. It is more permanent, and a special utility is required to create, modify, or delete them

31. File Directories and folders
Directory – list of files for each storage disk
Root directory – main directory
Subdirectory – smaller list subdivided from the root director
Folder
File specification (Path) – includes the drive letter, folder(s), file name, and extension.
File specification e.g. – C:\Music\Reggae\Marley One Love.mp3

32. File Directories and folders
File size – measured in bytes
OS keeps track of file sizes and supplies that information when you ask the list of the files
File date
File format – organization and layout of data that is stored in a file.
File header – section of data at the beginning of a file (date created, date updated, size, file type)
File format - E.g. graphics data can be stored in file formats such as bitmap, GIF, JPEG, or PNG.

33. FILE FORMATS (OS and Executable Extensions)
Type of File
Description
Extension
Batch file
Sequence of OS commands executed automatically when the comp boots
.bat
Configuration file
Info about program the comp uses to distribute the resources needed to run them
.cfg .sys .mif .bin .ini
Help
The info shown by on-screen Help
.hlp
Temporary file
A sort of scratch pad that has data while a file is open, but is discarded when you close the file
.tmp
Support prog
Program instructions executed along with the main .exe file for a prog
.ocx .vbx .vbs .dll
Program
Main executable files for a comp prog
.exe .com
File Extension is NOT the same as file format – extension is a good indicator of a file’s format

34. Data File Extensions Type of file Extensions Text
.txt .dat .rtf .doc (Microsoft Word 2004) .docx (Word 2007)
.odt (OpenDocument text) .wpd (WordPerfect)
Sound
.wav .mid .mp3 .mp4 .aac .au .ra(Real Audio)
Graphics
.bmp .pcx .tif .wmf .gif .jpg .png .eps .ai(Adobe Illustrator)
Animation/Video
.flc .fli .avi .mpg .mov(QuickTime) .rm(RealMedia) .wmv(Windows Media Player)
Web pages
.htm .html .asp .vml .php
Spreadsheets
.xls (Microsoft Excel 2003) .xlsx(Exel 2007) .ods(OpenDocument spreadsheet)
Database
.mdb (Microsoft Access) .odb(OpenOffice.org Base)
Miscallenous
.pdf (Adobe Acrobat) .ppt (Microsoft Powerpoint) .zip (WindZip) .pub (Microsoft Publisher) .qxp (QuarkXpress)

35. Why can’t I open files File damaged Someone changed the file extension
Some file formats exist in several variations, and your software might have the capability to open a particular variation of the format.
File damaged – corrupt by a transmission or disk error. You can use file recovery to repair
File extension changed – if a file contains a graphic, open with apps that do so

36. Converting a file from one format to another
Easiest way to convert a file
Open the file using that software, and then use the Export option, or Save As dialog box, to select a new file format, assign the file a new name and save it.
Some conversions DO NOT keep all the characteristics of the original file.

37. FILE MANAGEMENT OS helps you organize and manipulate your files from
within an application program
or by using a SPECIAL FILE MANAGEMENT UTILITY

38. Application-based file management
Apps provide a way to open files and save them in a specific folder in designated storage device
Some apps allow you to tag a file. File tag in Windows is a piece of information that describes the file

39. Save and Save As Option
Save As Option allows you to select a name and storage device for a file, whereas the Save option simply saves the latest version of a file under its current name and its current location

40. Save As option
Using apps, software interact with OS’s file management system when you’re opening and saving files
OS needs to know the name of a newly created file
Apps checks with the OS to get list of available files (searching)

41. FILE MANAGEMENT UTILITIES
OS provide file management utilities that shows you the files stored on your disks and lets you work with them
Mac OS X – Finder
Windows Vista – Explorer
Helps you view a list of files, find files, move files from one place to another, make copies of files, delete files, discover file properties, and rename files.

42. FILE MANAGEMENT METAPHORS
Logical storage models – metaphors that help you form a mental (logical) picture of the way in which files are stored
Filing cabinet
Tree structure
Microsoft programmer combined the filing cabinet metaphor with the tree structure metaphor in the WINDOWS EXPLORER FILE MANAGEMENT UTILITY

43. Tree Structure

44. Windows Explorer

45. Physical File Storage
OS help you visualize computer storage as files and folders
Physical storage model describes what really happens on the disks and in circuits
Before storing, the storage medium must be formatted
Formatting: process of dividing disk into tracks and sectors

46. Tracks and Sectors

47. OS keeping track of a file’s location
OS uses file system. Different systems use different file systems
Mac OS: Macitonsh Hierarchical File System Plus (HFS+)
Linux: Ext3fs (third extended file system)
Windows NT, 2000, Vista: New Technology File System (NTFS) Windows 95, 98, Me: FAT32

48. OS keeping track of a file’s location
To speed up the process of storing and retrieving data, a disk drive usually works with group of sectors called cluster or a “block”.
The number of sectors that form a cluster varies
A file system primary task is to maintain a list of clusters and keep track of which are empty and which hold data.

49. OS keeping track of a file’s location
This information is stored in a special index file
FAT32 file system: index file is called File Allocation table (FAT)
NTFS file system: index is called Master File Table (MFT)
If MFT or FAT is damaged or corrupted data can be lost. Important to backup.

50. OS keeping track of a file’s location
When you save a file, the operating system looks at the file allocation table to see what cluster is free.
Then it will update the allocation table to indicate that the file is saved in that cluster
If the file is too big to fit in one cluster, it will use more clusters that are next to it

51. MFT keeps track of file names and locations

52. Opening a file When you open a file,
The OS looks up the filename in the Master File Table.
It finds the correct cluster and sector on the hard drive
Then it moves the read-write head on the hard disk to that spot.
The read-write head will read that data
The data is sent back to the RAM for the OS to use

53. Deleting a file
If you want to delete a file, you might think that it is erased from the hard disk
Instead the master file table is updated to say that cluster is now empty and can be used for new data
There are programs that allow users to recover deleted items, because THEY ARE NOT REALLY DELETED
To really delete a file, you can use special “file shredder software”, that overwrites supposedly empty sectors with random 1s and 0s.

54. Can deleted files be undeleted?
The Windows Recycle Bin and similar utilities in other OS are designed to protect you from accidentally deleting hard disk files you actually need
Files in the Recycle Bin Folder can be undeleted so that they again appear in the regular directory.
The Recycle Bin can be emptied to permanently delete any files it contains.

55. Fragmentation
As computer writes files on a disk, parts of files tend to become scattered all over the disk and stored in noncontiguous clusters which refer to Fragmented files.
Drive performance generally declines as the read-write heads move back and fourth to locate the clusters containing the parts of a file.

56. Defragmentation
Defragmentation: a defragmenter rearrange the files on a disk so that they are stored in contiguous (adjacent or nearby) clusters.

57. Data Backup
It is often important to save your data in two places, in case one place goes bad.
Maybe your hard disk will break, your file system will break or your CD-ROM will get scratched
If you have important data, save it in another place, because you never know what will happen

58. Data Backup
You can make a backup of your entire computer (called full backup), but often it’s not worth it.
You can always re-install the operating system and get the applications you had before
The things you cannot replace are documents and files that you create. Those should be saved.

59. FILE COPIES AND SYNCHRONIZATION
File synchronization software: automatically make copies of files in specified folders. Ensures files in two or more locations contain the same data (E.g. Time Machine with Mac OS X)

60. File and system software
Backup software
Full backup: makes a fresh copy of every file in the folders you’ve specified for backup
Differential backup: makes a backup of only those files that were added or changed since your last full backup session
Incremental backup: makes a backup of the files that were added or changed since the last backup