Lecture 1: What is An OS Operating Systems (A) (Honor Track)

Operating Systems (A) (Honor Track)
Lecture 1: What is An OS
Tao Wang
School of Electronics Engineering and Computer Science
http://ceca.pku.edu.cn/wangtao
Fall 2012
Acknowledgements: Prof. Xiangqun Chen at PKU and Prof. Yuanyuan Zhou at UCSD
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A Typical Computer
from a Hardware Point of View
CPU
Memory
...
CPU
Chipset
Network
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Why do we need an OS?
A modern computer consists of:
•
•
•
•
•
One or more processors
Main memory
Disks
Printers
Various input/output devices
Managing all these components requires a layer of
software – the operating system
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What Is an OS?
“Code” that:

Sits between programs & hardware

Sits between different programs

Sits betweens different users
But what does it do?
to provide an orderly and controlled allocation of the processors,
memories and I/O devices among the various programs competing for
them
Real life analogy:
 Government?
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OS is…
 The
operating system is the software layer
between user applications and the hardware
 The
OS is “all the code that you didn’t have to
write” to implement your application ?
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And as an Extended Machine
Figure 1-2. Operating systems turn ugly hardware into beautiful
abstractions.
Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. All rights reserved. 0-13-6006639
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OS and Hardware
 The
OS abstracts/controls/mediates access to hardware
resources (what resources?)
 Computation (CPUs)
 Volatile storage (memory) and persistent storage (disk, etc.)
 Communication (network, modem, etc.)
 Input/output devices (keyboard, display, printer, camera, etc.)
 The
OS defines a set of logical resources (objects) and a set of
well-defined operations on those objects (interfaces)
 Physical resources (CPU and memory)
 Logical resources (files, programs, names)
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Benefits to Applications
 Simpler
 no tweaking device registers
 Device
independent
 all network cards look the same
 Portable
 Across
Windows95/98/ME/NT/2000/XP/Vista/Windows 7
 Worry
less about interference from other
applications
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What does an OS do?
Resources
Services
 Allocation
 Abstraction
 Protection
 Simplification
 Reclamation
 Convenience
 Virtualization
 Standardization
Makes computers simpler
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What Is an OS?
Government
Resources
Finite resources
 Allocation
Competing demands
Land,
 Protection
 Reclamation
 Virtualization
Limited budget,
Examples:
Oil,

CPU
Gas,

Memory
…

Disk

Network
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What Is an OS?
Government
Resources
 Allocation
You can’t hurt me
I can’t hurt you
Law and order
 Protection
 Reclamation
 Virtualization
Implies some degree of
safety & security
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What Is an OS?
Government
Resources
 Allocation
The OS giveth
The OS taketh away
Income Tax
 Protection
 Reclamation
 Virtualization
Voluntary at run time
Implied at termination
Involuntary
Cooperative
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What Is an OS?
Government
Resources
 Allocation
Illusion of infinite,
private resources
Social security
 Protection
 Reclamation
Memory versus disk
Timeshared CPU
 Virtualization
More extreme cases
possible (& exist)
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Some Questions to Ponder
 What
is part of an OS? What is not? Is the window system
part of an OS? Java?
 Popular
OSes today are Windows, Linux, and OS X
 How different/similar do you think these OSes are?
 Somewhat
surprisingly, OSes change all of the time
 Consider the series of releases of NT, Linux, OS X…
 What are the drivers of OS change?
• New hardware, new applications
 What
are the most compelling issues facing OSes today?
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Summary
 Why
do we need an OS?
 What
 Next
does an OS do?
lecture: OS History
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