Two Directions: – Practical. • Linux+ Guide to Linux Certification and Lab Manual.
• Lab Experience. – Theoretical. • Operating Systems (3rd Edition Gary Nutt).
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Computer Systems II Gordon College
Operating System Overview
Class Intro
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• Operating System Class • Two Directions: – Practical • Linux+ Guide to Linux Certification and Lab Manual • Lab Experience
– Theoretical • Operating Systems (3rd Edition Gary Nutt) • Lecture and Projects
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Why Study Operating Systems?
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• Understand the model of operation – Easier to see how to use the system – Enables you to write efficient code
• Learn to design an OS • Even so, OS is pure overhead of real work • Application programs have the real value to person who buys the computer
Perspectives of the Computer print cut send save
open() malloc() fork()
read-disk
start-printer track-mouse
Application Software System Software
Application Software System Software
Application Software System Software
Hardware
Hardware
Hardware
(b) Application Programmer View
(c) OS Programmer View
(a) End User View
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System Software
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•Independent of individual applications, but common to all of them •Examples –C library functions –A window system –A database management system –Resource management functions –The OS
Using the System Software
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Application Programmer
System Software
Software API Command Line Interpreter Compiler
Loader Libraries Libraries Libraries
Database Management System
Window System
OS
Hardware
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Application Software, System Software, and the OS
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Human-Computer Interface Application Software API System Software (More Abstract Resources) OS Interface Trusted OS (Abstract Resources) Software-Hardware Interface Hardware Resources
The OS as Resource Manager
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•Process: An executing program •Resource: Anything that is needed for a process to run –Memory –Space on a disk –The CPU
•“An OS creates resource abstractions” •“An OS manages resource sharing”
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Resource Abstraction
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load(block, length, device); seek(device, 236); out(device, 9) write(char *block, int len, int device, int track, int sector) { ... load(block, length, device); seek(device, 236); out(device, 9); ... } write(char *block, int len, int device,int addr); fprintf(fileID, “%d”, datum);
Disk Abstractions
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Application Programmer OS Programmer
load(…); seek(…); out(…);
(a) Direct Control
void write() { load(…); seek(…) out(…) }
(b) write() abstraction
int fprintf(…) { ... write(…) … }
(c) fprintf() abstraction
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Abstract Resources
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User Interface Application Abstract Resources (API) Middleware OS Resources (OS Interface) OS Hardware Resources
Abstract Machines
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Abstract Machines
Idea Program
Physical Machine
Result
Idea
Program
…
Result
…
Idea
…
Program
Result
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Resource Sharing
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• Space- vs time-multiplexed sharing • To control sharing, must be able to isolate resources • OS usually provides mechanism to isolate, then selectively allows sharing – How to isolate resources – How to be sure that sharing is acceptable
• Concurrency
The OS as a Conductor
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The OS coordinates the sharing and use of all the components in the computer
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Multiprogramming Abstract Machine Pi
Abstract Machine Pj
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Abstract Machine Pk
… OS Resource Sharing
Pi Memory Pk Memory
…
Time-multiplexed Physical Processor
Pj Memory
Space-multiplexed Physical Memory
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Multiprogramming(2) • Technique for sharing the CPU among runnable processes – Process may be blocked on I/O – Process may be blocked waiting for other resource, including the CPU
• While one process is blocked, another might be able to run • Multiprogramming OS accomplishes CPU sharing “automatically” – scheduling • Reduces time to run all processes
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How Multiprogramming Works
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Process 1 Process 2 Process 3
Time-multiplexed CPU Process 4
Space-multiplexed Memory
Speeding Up the Car Wash Vacuum Inside
Wash
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Dry
(a) The Sequential Car Wash
Vacuum Inside Wash
Dry
(b) The Parallel Car Wash
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Multiprogramming Performance Pi’s Total Execution Time, ti 0
ti
Time
(a) Pi’s Use of Machine Resources P1 P2
…
Pi
…
PN
Time
(a) All Processes’ Use of Machine Resources Using the processor I/O operation
OS Strategies • • • • • • •
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Batch processing Timesharing Personal computer & workstations Process control & real-time Network Distributed Small computers
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Batch Processing
Job 3
Job 19
Input Spooler
Output Spooler
Input Spool
Batch Processing(2) • • • • • • •
Output Spool
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Uses multiprogramming Job (file of OS commands) prepared offline Batch of jobs given to OS at one time OS processes jobs one-after-the-other No human-computer interaction OS optimizes resource utilization Batch processing (as an option) still used today
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A Shell Script Batch File
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cc -g -c menu.c cc -g -o driver driver.c menu.o driver < test_data > test_out lpr -PthePrinter test_out tar cvf driver_test.tar menu.c driver.c test_data test_out uuencode driver_test.tar driver_test.tar >driver_test.encode
Timesharing Systems
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Abstract Machines Result Physical Machine
Command
Result
…
Command
Result Command
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Timesharing Systems(2)
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Computer Research Corp ‘67
• Uses multiprogramming • Support interactive computing model (Illusion of multiple consoles) • Different scheduling & memory allocation strategies than batch • Tends to propagate processes • Considerable attention to resource isolation (security & protection) • Tend to optimize response time
Personal Computers
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• CPU sharing among one person’s processes • Power of computing for personal tasks – Graphics – Multimedia
• Trend toward very small OS • OS focus on resource abstraction • Rapidly evolved to “personal multitasking” systems
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Process Control & Real-Time
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• Computer is dedicated to a single purpose • Classic embedded system • Must respond to external stimuli in fixed time • Continuous media popularizing real-time techniques • An area of growing interest
Networks
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• LAN (Local Area Network) evolution • 3Mbps (1975) → 10 Mbps (1980) → 100 Mbps (1990) → 1 Gbps (2000) • High speed communication means new way to do computing – – – –
Shared files Shared memory Shared procedures/objects ???
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Distributed OS
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• Wave of the future App App
App
App App
App
Distributed OS
Multiple Computers connected by a Network
Small Computers
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• PDAs, STBs, embedded systems became commercially significant • Have an OS, but – Not general purpose – Limited hardware resources – Different kinds of devices • Touch screen, no keyboard • Graffiti
– Evolving & leading to new class of Oses
• PalmOS, Pocket PC (WinCE), VxWorks, …
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Evolution of Modern OS Timesharing Memory Mgmt Scheduling Batch Protection Memory Mgmt Protection Scheduling Files Devices
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Network OS PC & Wkstation System software
Client-Server Model Protocols
Real-Time
Human-Computer Interface
Scheduling
Small Computer Modern OS
Network storage, Resource management
Examples of Modern OS
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• UNIX variants (e.g. Linux) -- have evolved since 1970 • Windows NT/2K -- has evolved since 1989 (much more modern than UNIX – Win2K = WinNT, V5
• Research OSes – still evolving … • Small computer OSes – still evolving …
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The Microsoft OS Family
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Win32 API Win32 API Subset Win32 API SubSet Windows CE (Pocket PC) Windows 95/98/Me
Windows NT/2000/XP
Summary
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An Operating System must be able to: • provide functionality to apps • provide abstraction of hardware to users and apps • provide the sharing of resources to processes • provide security and protection • be as transparent as possible • be as light as possible
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