Chapter 4: What is an operating system?

What is an operating system? A program or collection of programs that coordinate computer usage among users and handle common tasks. A program or collection of programs that coordinate computer usage among users and handle common tasks.

OS - functions 1. Hide details of input and output 2. Provide an environment for multiple users/programs to work concurrently – multitasking and multi-slacking 3. Allocate memory to different users/programs 4. Share resources (files, printer) among users 5. Provide means for users/programs to communicate with each other 6. Provide protection and security for programs

OS functions - examples 1. You can access disks as file cabinets without the knowledge of tracks, sector, etc – hide I/O details 2. You can work with multiple programs at the same time, e.g., using IE to download files and use Word to write a report - multitasking 3. In STT475 and 375, we share the same printers – share resources 4. You can interact with machines via the Internet – communicate among users/machines 5. When you use password on your machine, no can use your computer without the password - protection

Why are there difference OS’s? Different types of cars for different purposes Different types of cars for different purposes –Vans for family –Compact cars for gas mileage –SUV for rough terrains Different OS’s for different environments and applications Different OS’s for different environments and applications –Windows 2000/XP for personal computers –Windows 2003 Servers for web servers and big corporations –Unix/Linux for personal computers and servers

What is “multitasking”? The speed of CPUs is much faster than any I/O device The speed of CPUs is much faster than any I/O device –If a computer only execute one program (e.g., Word) from beginning to end, the CPU would stay idle most the time since no human can type fast enough. Multitasking allows multiple programs to reside in the memory/virtual memory at the same and switch the CPU between those programs Multitasking allows multiple programs to reside in the memory/virtual memory at the same and switch the CPU between those programs

Why OS’s need to coordinate programs? Printing example Printing example –When you print a Word document and a webpage at the same time on your home printer, did you ever find that one is printed in mid of another? The OS determines which program uses the printer first and then next program The OS determines which program uses the printer first and then next program Memory example Memory example –When you use Word and IE at the same time, the OS must allocate memory space for both programs

What is “booting”? Start up the computer and allow the OS to set up itself Start up the computer and allow the OS to set up itself Then the OS starts behind-the-scenes programs (services) for special tasks Then the OS starts behind-the-scenes programs (services) for special tasks –Monitoring , coordinating printing requests, monitoring data on the network.

What can’t Windows read Mac or Linux disks Different OS’s define tracks and sectors differently on the disk – formatting Different OS’s define tracks and sectors differently on the disk – formatting Windows machines do not know how to interpret Mac’s format Windows machines do not know how to interpret Mac’s format Today, Mac machines can read Windows disks is because that Mac OS tries to read disks in Windows format after it fails to read it in Mac’s format. Today, Mac machines can read Windows disks is because that Mac OS tries to read disks in Windows format after it fails to read it in Mac’s format.

Portable storage devices Floppy disks Floppy disks –Limited capacity, very slow, not reliable –Most of today’s PC’s do not even install floppy disk drives Jumpdrive, pin drive, USB memory stick, flash memory, etc Jumpdrive, pin drive, USB memory stick, flash memory, etc –High capacity, fast, and reliable –Use USB connection

What is “reboot”? Stop all current processing and Stop all current processing and Restart the computer Restart the computer If everything were perfect in a computer, reboot would not be needed If everything were perfect in a computer, reboot would not be needed Reboot sometime is the most efficient way to restore the computer back to normal Reboot sometime is the most efficient way to restore the computer back to normal Reboot is the only way to restore the system when the computer does not respond to any keystroke and mouse Reboot is the only way to restore the system when the computer does not respond to any keystroke and mouse

Which OS is best? Three most common OS’s Three most common OS’s –Windows by Microsoft Aggressively marketed Aggressively marketed Take a large fraction of individual stations Take a large fraction of individual stations As a result, users can easily share programs and data As a result, users can easily share programs and data –Macintosh OS X by Apple Offers a simple, clean, and powerful graphical user interface Offers a simple, clean, and powerful graphical user interface –Linux by Linus Torvalds and others Offer higher reliability and ability to link complex tasks Offer higher reliability and ability to link complex tasks

Summary – chapter 4 Operating systems handle common tasks Operating systems handle common tasks –Identify one user from another –Scheduling and coordinating processing –Allocating resources (RAM, CPU time, printer, etc) to programs Multitasking allows a computer to split its CPU time and resources among multiple programs and users Multitasking allows a computer to split its CPU time and resources among multiple programs and users Booting restarts the computer and the OS sets up the environment Booting restarts the computer and the OS sets up the environment Rebooting involves shutting down the computer and starting it up again Rebooting involves shutting down the computer and starting it up again Different OS’s are designed for different purposes Different OS’s are designed for different purposes Different OS’s define different formats on disks Different OS’s define different formats on disks

Terminology Operating systems Operating systems Booting a computer Booting a computer Rebooting a computer Rebooting a computer Single-tasking Single-tasking Multitasking Multitasking MS Windows MS Windows Mac OS X Mac OS X Linux Linux