Chapter Chapter 44: : What is an What is an operating systemoperating system??

What is an operating What is an operating system?system?

A program or collection of A program or collection of programs that coordinate programs that coordinate computer usage among users and computer usage among users and handle common tasks.handle common tasks.

OS - functionsOS - functions

1.1. Hide details of input and outputHide details of input and output2.2. Provide an environment for multiple Provide an environment for multiple

users/programs to work concurrently users/programs to work concurrently – multitasking and multi-slacking– multitasking and multi-slacking

3.3. Allocate memory to different Allocate memory to different users/programsusers/programs

4.4. Share resources (files, printer) among Share resources (files, printer) among usersusers

5.5. Provide means for users/programs to Provide means for users/programs to communicate with each othercommunicate with each other

6.6. Provide protection and security for Provide protection and security for programsprograms

OS functions - examplesOS functions - examples

1.1. You can access disks as file cabinets without You can access disks as file cabinets without the knowledge of tracks, sector, etc – the knowledge of tracks, sector, etc – hide I/O hide I/O detailsdetails

2.2. You can work with multiple programs at the You can work with multiple programs at the same time, e.g., using IE to download files and same time, e.g., using IE to download files and use Word to write a report - use Word to write a report - multitaskingmultitasking

3.3. In STT475 and 375, we share the same printers In STT475 and 375, we share the same printers – – share resourcesshare resources

4.4. You can interact with machines via the Internet You can interact with machines via the Internet – – communicate among users/machinescommunicate among users/machines

5.5. When you use password on your machine, no When you use password on your machine, no can use your computer without the password - can use your computer without the password - protectionprotection

Why are there difference Why are there difference OS’s?OS’s?

Different types of cars for different Different types of cars for different purposespurposes– Vans for familyVans for family– Compact cars for gas mileageCompact cars for gas mileage– SUV for rough terrains SUV for rough terrains

Different OS’s for different environments Different OS’s for different environments and applicationsand applications– Windows 2000/XP for personal computersWindows 2000/XP for personal computers– Windows 2003 Servers for web servers and Windows 2003 Servers for web servers and

big corporationsbig corporations– Unix/Linux for personal computers and serversUnix/Linux for personal computers and servers

What is “multitasking”?What is “multitasking”?

The speed of CPUs is much faster than The speed of CPUs is much faster than any I/O deviceany I/O device– If a computer only execute one program If a computer only execute one program

(e.g., Word) from beginning to end, the (e.g., Word) from beginning to end, the CPU would stay idle most the time since CPU would stay idle most the time since no human can type fast enough.no human can type fast enough.

Multitasking allows multiple programs Multitasking allows multiple programs to reside in the memory/virtual to reside in the memory/virtual memory at the same and switch the memory at the same and switch the CPU between those programsCPU between those programs

Why OS’s need to Why OS’s need to coordinate programs?coordinate programs?

Printing examplePrinting example– When you print a Word document and a When you print a Word document and a

webpage at the same time on your home webpage at the same time on your home printer, did you ever find that one is printer, did you ever find that one is printed in mid of another?printed in mid of another?

The OS determines which program uses the The OS determines which program uses the printer first and then next programprinter first and then next program

Memory exampleMemory example– When you use Word and IE at the same When you use Word and IE at the same

time, the OS must allocate memory space time, the OS must allocate memory space for both programsfor both programs

What is “booting”?What is “booting”?

Start up the computer and allow Start up the computer and allow the OS to set up itselfthe OS to set up itself

Then the OS starts behind-the-Then the OS starts behind-the-scenes programs (services) for scenes programs (services) for special tasksspecial tasks– Monitoring email, coordinating Monitoring email, coordinating

printing requests, monitoring data printing requests, monitoring data on the network.on the network.

What can’t Windows read What can’t Windows read Mac or Linux disksMac or Linux disks

Different OS’s define tracks and Different OS’s define tracks and sectors differently on the disk – sectors differently on the disk – formattingformatting

Windows machines do not know how Windows machines do not know how to interpret Mac’s formatto interpret Mac’s format

Today, Mac machines can read Today, Mac machines can read Windows disks is because that Mac OS Windows disks is because that Mac OS tries to read disks in Windows format tries to read disks in Windows format after it fails to read it in Mac’s format.after it fails to read it in Mac’s format.

Portable storage devicesPortable storage devices

Floppy disksFloppy disks– Limited capacity, very slow, not Limited capacity, very slow, not

reliablereliable– Most of today’s PC’s do not even Most of today’s PC’s do not even

install floppy disk drivesinstall floppy disk drives Jumpdrive, pin drive, USB Jumpdrive, pin drive, USB

memory stick, flash memory, etcmemory stick, flash memory, etc– High capacity, fast, and reliableHigh capacity, fast, and reliable– Use USB connectionUse USB connection

What is “reboot”?What is “reboot”?

Stop all current processing andStop all current processing and Restart the computerRestart the computer If everything were perfect in a If everything were perfect in a

computer, reboot would not be neededcomputer, reboot would not be needed Reboot sometime is the most efficient Reboot sometime is the most efficient

way to restore the computer back to way to restore the computer back to normalnormal

Reboot is the only way to restore the Reboot is the only way to restore the system when the computer does not system when the computer does not respond to any keystroke and mouserespond to any keystroke and mouse

Which OS is best?Which OS is best?

Three most common OS’sThree most common OS’s– Windows by MicrosoftWindows by Microsoft

Aggressively marketedAggressively marketed Take a large fraction of individual stationsTake a large fraction of individual stations As a result, users can easily share programs and As a result, users can easily share programs and

datadata

– Macintosh OS X by AppleMacintosh OS X by Apple Offers a simple, clean, and powerful graphical user Offers a simple, clean, and powerful graphical user

interfaceinterface

– Linux by Linus Torvalds and others Linux by Linus Torvalds and others Offer higher reliability and ability to link complex Offer higher reliability and ability to link complex

taskstasks

Summary – chapter 4Summary – chapter 4

Operating systems handle common tasksOperating systems handle common tasks– Identify one user from anotherIdentify one user from another– Scheduling and coordinating processing Scheduling and coordinating processing – Allocating resources (RAM, CPU time, printer, etc) to Allocating resources (RAM, CPU time, printer, etc) to

programsprograms Multitasking allows a computer to split its CPU Multitasking allows a computer to split its CPU

time and resources among multiple programs time and resources among multiple programs and usersand users

Booting restarts the computer and the OS sets Booting restarts the computer and the OS sets up the environmentup the environment

Rebooting involves shutting down the computer Rebooting involves shutting down the computer and starting it up againand starting it up again

Different OS’s are designed for different Different OS’s are designed for different purposespurposes

Different OS’s define different formats on disksDifferent OS’s define different formats on disks

TerminologyTerminology

Operating systemsOperating systems Booting a Booting a

computercomputer Rebooting a Rebooting a

computercomputer Single-taskingSingle-tasking MultitaskingMultitasking

MS WindowsMS Windows Mac OS XMac OS X LinuxLinux