Transcript What is an operating system?

Chapter 4: What is an
operating system?
What is an operating system?
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A program or collection of programs
that coordinate computer usage
among users and handle common
tasks.
OS - functions
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Hide details of input and output
Provide an environment for multiple
users/programs to work concurrently –
multitasking and multi-slacking
Allocate memory to different
users/programs
Share resources (files, printer) among
users
Provide means for users/programs to
communicate with each other
Provide protection and security for
programs
OS functions - examples
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You can access disks as file cabinets without the
knowledge of tracks, sector, etc – hide I/O details
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
In STT475 and 375, we share the same printers –
share resources
You can interact with machines via the Internet –
communicate among users/machines
When you use password on your machine, no one
can use your computer without the password protection
Why are there difference OS’s?
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Different types of cars for different purposes
– Vans for family
– Compact cars for gas mileage
– SUV for rough terrains
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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”?
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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.
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Multitasking allows multiple programs to
reside in the memory/virtual memory at the
same time and switch the CPU between
those programs
Why OS’s need to coordinate
programs?
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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
the other?
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The OS determines which program uses the printer
first and then next program
Memory example
– When you use Word and IE at the same time,
the OS must allocate memory space for both
programs
What is “booting”?
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Start up the computer and allow the
OS to set up itself
Then the OS starts behind-the-scenes
programs (services) for special tasks
– Monitoring email, coordinating printing
requests, monitoring data on the
network.
What can’t Windows read Mac
or Linux disks
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Different OS’s define tracks and sectors
differently on the disk – formatting
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.
Portable storage devices
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Floppy disks
– Limited capacity, very slow, not reliable
– Most of today’s PC’s do not even install
floppy disk drives
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Jumpdrive, pin drive, USB memory
stick, flash memory, etc
– High capacity, fast, and reliable
– Use USB connection
What is “reboot”?
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Stop all current processing and
Restart the computer
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 is the only way to restore the
system when the computer does not
respond to any keystroke and mouse
Which OS is best?
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Three most common OS’s
– Windows by Microsoft
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Aggressively marketed
Take a large fraction of individual stations
As a result, users can easily share programs and data
– Macintosh OS X by Apple
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Offers a simple, clean, and powerful graphical user
interface
– Linux by Linus Torvalds and others
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Offer higher reliability and ability to link complex tasks
Summary – chapter 4
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Operating systems handle common tasks
– Identify one user from another
– Scheduling and coordinating processing
– Allocating resources (RAM, CPU time, printer, etc) to
programs
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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
Rebooting involves shutting down the computer and
starting it up again
Different OS’s are designed for different purposes
Different OS’s define different formats on disks
Terminology
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Operating systems
Booting a computer
Rebooting a
computer
Single-tasking
Multitasking
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MS Windows
Mac OS X
Linux