overview of operating systems ahmed...
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Overview of Operating Systems
Ahmed Tawfik
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Silberschatz, Galvin and Gagne 20021.2Operating System Concepts
Operating Systems Fundamentals
� Modern Operating Systems are increasingly complex✔ Operating System Millions of Lines of Code
– DOS 0.015– Windows 95 11– Windows 98 18– Windows NT 28– Windows 2000 35
� Modern Operating Systems offer advanced functionality✦ Control a wide range of devices✦ Coordinate the activities of users and programs✦ Give the illusion of infinite resources
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Silberschatz, Galvin and Gagne 20021.3Operating System Concepts
Focus
� Process Management✦ Processes✦ Threads✦ Scheduling✦ Inter-process synchronization✦ Deadlock prevention
� Storage Management✦ Memory Management✦ Virtual Memory✦ File Systems
� Optional Topics✦ I/O Systems✦ Security and Protection
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Silberschatz, Galvin and Gagne 20021.4Operating System Concepts
What is an Operating System?
� A program that acts as an intermediary between a user ofa computer and the computer hardware.
� Operating system goals:✦ Execute user programs and make solving user problems
easier.✦ Make the computer system convenient to use.
� Use the computer hardware in an efficient manner.
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Silberschatz, Galvin and Gagne 20021.5Operating System Concepts
Chapter 1: Introduction
� What is an Operating System?� Mainframe Systems� Desktop Systems� Multiprocessor Systems� Distributed Systems� Clustered System� Real -Time Systems� Handheld Systems� Computing Environments
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Silberschatz, Galvin and Gagne 20021.6Operating System Concepts
Computer System Components
1. Hardware – provides basic computing resources (CPU,memory, I/O devices).
2. Operating system – controls and coordinates the use ofthe hardware among the various application programs forthe various users.
3. Applications programs – define the ways in which thesystem resources are used to solve the computingproblems of the users (compilers, database systems,video games, business programs).
4. Users (people, machines, other computers).
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Silberschatz, Galvin and Gagne 20021.7Operating System Concepts
Abstract View of System Components
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Silberschatz, Galvin and Gagne 20021.8Operating System Concepts
Operating System Definitions
� Resource allocator – manages and allocates resources.� Control program – controls the execution of user
programs and operations of I/O devices .� Kernel – the one program running at all times (all else
being application programs).
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Silberschatz, Galvin and Gagne 20021.9Operating System Concepts
Mainframe Systems
� Reduce setup time by batching similar jobs� Automatic job sequencing – automatically transfers control from
one job to another. First rudimentary operating system.� Resident monitor
✦ initial control in monitor✦ control transfers to job✦ when job completes control transfers pack to monitor
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Silberschatz, Galvin and Gagne 20021.10Operating System Concepts
Memory Layout for a Simple Batch System
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Silberschatz, Galvin and Gagne 20021.11Operating System Concepts
Multiprogrammed Batch Systems
Several jobs are kept in main memory at the same time, and theCPU is multiplexed among them.
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Silberschatz, Galvin and Gagne 20021.12Operating System Concepts
OS Features Needed for Multiprogramming
� I/O routine supplied by the system.� Memory management – the system must allocate the
memory to several jobs.� CPU scheduling – the system must choose among
several jobs ready to run.� Allocation of devices.
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Silberschatz, Galvin and Gagne 20021.13Operating System Concepts
Time-Sharing Systems–Interactive Computing
� The CPU is multiplexed among several jobs that are keptin memory and on disk (the CPU is allocated to a job onlyif the job is in memory).
� A job swapped in and out of memory to the disk.� On-line communication between the user and the system
is provided; when the operating system finishes theexecution of one command, it seeks the next “controlstatement” from the user’s keyboard.
� On-line system must be available for users to access dataand code.
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Silberschatz, Galvin and Gagne 20021.14Operating System Concepts
Desktop Systems
� Personal computers – computer system dedicated to asingle user.
� I/O devices – keyboards, mice, display screens, smallprinters.
� User convenience and responsiveness.� Can adopt technology developed for larger operating
system’ often individuals have sole use of computer anddo not need advanced CPU utilization of protectionfeatures.
� May run several different types of operating systems(Windows, MacOS, UNIX, Linux)
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Silberschatz, Galvin and Gagne 20021.15Operating System Concepts
Parallel Systems
� Multiprocessor systems with more than on CPU in closecommunication.
� Tightly coupled system – processors share memory and aclock; communication usually takes place through theshared memory.
� Advantages of parallel system:✦ Increased throughput✦ Economical✦ Increased reliability
✔ graceful degradation✔ fail-soft systems
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Silberschatz, Galvin and Gagne 20021.16Operating System Concepts
Parallel Systems (Cont.)
� Symmetric multiprocessing (SMP)✦ Each processor runs and identical copy of the operating
system.✦ Many processes can run at once without performance
deterioration.✦ Most modern operating systems support SMP
� Asymmetric multiprocessing✦ Each processor is assigned a specific task; master
processor schedules and allocated work to slaveprocessors.
✦ More common in extremely large systems
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Silberschatz, Galvin and Gagne 20021.17Operating System Concepts
Symmetric Multiprocessing Architecture
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Silberschatz, Galvin and Gagne 20021.18Operating System Concepts
Distributed Systems
� Distribute the computation among several physicalprocessors.
� Loosely coupled system – each processor has its ownlocal memory; processors communicate with one anotherthrough various communications lines, such as high-speed buses or telephone lines.
� Advantages of distributed systems.✦ Resources Sharing✦ Computation speed up – load sharing✦ Reliability✦ Communications
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Silberschatz, Galvin and Gagne 20021.19Operating System Concepts
Distributed Systems (cont)
� Requires networking infrastructure.� Local area networks (LAN) or Wide area networks (WAN)� May be either client-server or peer-to-peer systems.
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Silberschatz, Galvin and Gagne 20021.20Operating System Concepts
General Structure of Client-Server
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Silberschatz, Galvin and Gagne 20021.21Operating System Concepts
Clustered Systems
� Clustering allows two or more systems to share storage.� Provides high reliability.� Asymmetric clustering: one server runs the application
while other servers standby.� Symmetric clustering: all N hosts are running the
application.
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Silberschatz, Galvin and Gagne 20021.22Operating System Concepts
Real-Time Systems
� Often used as a control device in a dedicated applicationsuch as controlling scientific experiments, medicalimaging systems, industrial control systems, and somedisplay systems.
� Well-defined fixed-time constraints.� Real-Time systems may be either hard or soft real-time.
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Silberschatz, Galvin and Gagne 20021.23Operating System Concepts
Real-Time Systems (Cont.)
� Hard real-time:✦ Secondary storage limited or absent, data stored in
short term memory, or read-only memory (ROM)✦ Conflicts with time-sharing systems, not supported by
general-purpose operating systems.
� Soft real-time✦ Limited utility in industrial control of robotics✦ Useful in applications (multimedia, virtual reality)
requiring advanced operating-system features.
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Silberschatz, Galvin and Gagne 20021.24Operating System Concepts
Handheld Systems
� Personal Digital Assistants (PDAs)� Cellular telephones� Issues:
✦ Limited memory✦ Slow processors✦ Small display screens.
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Silberschatz, Galvin and Gagne 20021.25Operating System Concepts
Migration of Operating-System Concepts and Features
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Silberschatz, Galvin and Gagne 20021.26Operating System Concepts
Computing Environments
� Traditional computing� Web-Based Computing� Embedded Computing