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Examples of Operating Systems.
What is an operating system?
Windows 95Windows XP
Windows Vista
Unix
MS-DOS
Acorn MOS
Mac OS
OSX
Linux
Android (open handset alliance)
Symbian
Windows Mobile
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What is an operating system?
• What does it do? • Process Management• Memory management• I/O management• Support functions• Networking• User interface• Security
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Implementation
Where does it fit in?
Application
Instruction Level
Program
Operating System
Micro architecture
Instruction Set Architecture
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Operating System Goals
• Efficiency
• Throughput
• Functionality
• Robustness
• Extensibility
• Portability
• Security
• Interactivity
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Concepts
• Architectures of Operating Systems– Monolithic– Layered– Kernel– Microkernel– Virtual Machines
• Increasing Efficiency– Multi program– Multi User
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Monolithic Architecture
• Monolithic Architecture—the early operating systems
– Every component is contained in the kernel, can directly communicate with other components
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Monolithic Architecture
Computer Hardware
OS Layer
User SpaceApplications
System Calls
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Monolithic Architecture
• Pros– Highly efficient – by direct intercommunication
between components
• Cons– difficult to develop– difficult to isolate the source of bugs and other
errors • particularly susceptible to damage from malicious
code
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Layered Architecture• Layered OS structure:
– Group components that perform similar functions into layers. Each layer communicates only with neighbour layer
Computer Hardware
Kernel Space
User Space
Layer 3
Layer 2
Layer 1
Layer 0
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Layered Architecture
• Pros– It provides good modularity – helps simplify
the development of an OS
• Cons– Less efficient– Complex design – each functionality has to be
divided into parts to fit into different layers.
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Kernel Based Architecture
• It separates the machine-independent parts from the machine-dependent parts– Kernel is machine-dependent. It contains the
basic component of OS.
Computer Hardware
Operating System
User Space
OS Kernel
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Kernel Based Architecture
• Pros– Better portability—Kernel encloses all the
machine-dependent code
• Cons– Suffers similar problem as in layered OSs
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Microkernel Based Architecture
• As OS expanded, the kernel became large and difficult to manage– Microkernel approach removes all
nonessential components from the kernel and implementing them as system and user-level programs.
• Result: A smaller kernel
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Microkernel Based Architecture
Computer Hardware
Operating System
User Space
Microkernel
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Microkernel Based Architecture
• Pros– Enhance portability, extensibility, reliability
and security
• Cons– Less efficient—increased system function
overhead
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Virtual Machines
• Can create the illusion that there are more than one separate machines.
Computer Hardware
Virtual machine implementation
Kernel
User Space
VM1
Kernel
User Space
VM1
User Space
Host Operating System
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Increasing Efficiency
• Multiprogramming– Try to Keep the CPU busy– CPU operations take less
time than I/O– When a process waits for
I/O operation, OS swaps to another process.
OperatingSystem
Job 1
Job 2
Job 3
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Multi User
– Logical extension of Multiprogramming