Operating Systems

Unit 1:– OS objectives– Mode of operation– Components– Architecture– Linux– Windows XP

Operating Systems

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What Is an Operating System?

• Computer = set of able resources– processor(s), memory, I/O & communication

devices• OS

– enables use of resources– manages resources

• resources not limited to hardware• shift from:

– pure efficient use of resources to– enhance user experience

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Mode of operation• Kernel:

– substance, core, center, essence, gist, heart, heart and soul, inwardness, marrow, meat, nub, pith, sum, nitty-gritty

• pieces of software that perform OS tasks

• has privileged access to resources

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Terminology• kernel mode or kernel space

• user mode or user space

• system call: – user mode program invokes kernel

mode functionality

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Operating System Components

• Processor scheduler• Memory manager• I/O manager• Interprocess communication

manager• File system manager

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Operating System Architectures

• Operating systems tend to be complex– Provide many services – Support variety of hardware and software– Operating system architectures help

manage this complexity• Organize operating system components• Specify privilege with which each component

executes

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Operating System Architectures

• monolithic• layered• micro-kernel• distributed

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Monolithic Architecture• Monolithic operating system

– Every component contained in kernel• direct communication among all elements• highly efficient

– Problems:• complexity• new devices, emerging technologies

– enabling, protection

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Monolithic Architecture

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Layered Architecture• Groups components that perform

similar functions into layers• Each layer communicates only

with adjacent layer• System calls might pass through

many layers before completion

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Layered Architecture

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Microkernel Architecture• Microkernel

– provides only small number of services– attempt to keep kernel small and

scalable• High degree of modularity

• Extensible, portable and scalable• Increased level of inter-module

communication

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Microkernel Architecture

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Distributed Operating Systems

• Network operating system– Runs on one computer but allows its

processes to access remote resources

• Distributed operating system– Single OS manages resources on more

than one computer

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Distributed Operating Systems

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Linux Kernel Architecture• Monolithic kernel:

Contains modular components– Process management– Interprocess communication– Memory management– File system management

• VFS: provides a single file system interface– I/O management– Networking

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Linux Kernel Architecture

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Loadable Kernel Modules• Enables code to be loaded on

demand• Reduces the kernel’s memory footprint

– Kmod: a kernel subsystem that manages modules without user intervention• Determines module dependencies and loads

and unloads them on demand – Problem: kernel and module versions

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• Modified microkernel – has layers– has modular components within layer

– Microkernel• Basic system mechanisms• Thread scheduling, interrupt dispatching, etc.• Abstracts hardware specifics that differ

between architectures

Windows XP Kernel Architecture

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Windows XP Kernel Architecture

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• Executive– main operating system subsystems

• Environment subsystems– Provide a specific computing

environment for user-mode processes:– Examples: Win32, SFU, WOW64

Windows XP Kernel Architecture

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Agenda for next week:

• Chapter 3: Process Concepts• Chapter 4: Thread Concepts

• Read ahead !