Principles of Operating Systems:Design & Applications

Chapter 1

Introduction to Operating Systems

Objectives

be able to discuss ways of defining the operating system

understand the different roles the OS plays have a general picture of the areas of OS

responsibility have a general understanding of the evolution

of operating systems

Objectives (cont.)

understand some of the general trends in OS development

be able to describe the bootstrapping process understand how system calls work

What is an Operating System?

Everything in the distribution? Just the kernel? Our working definition: The kernel and any

programs necessary to provide services to applications

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What is an Operating System?

Manages the hardware resources among competing entities

Provides common services to applications Interfaces applications to hardware

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Resource Manager

Allocates scarce resources Protects entities from interfering with each other Protects itself and the overall system from both

malicious and accidental damage Programs run at the pleasure of the OS

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Service Provider

Provides common functionality, simplifying applications

Provides standard interfaces, making applications more consistent

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Virtual Machine

Defines a number of characteristics not found on the hardware

Presents a cleaner and easier “machine” for applications to run on

Hides the boundary between OS and hardware, allowing flexibility in hardware design while still running the same programs

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Areas of OS Responsibility

Hardware CPU Memory I/O Devices

File Systems Security

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Areas of OS Responsibility

Others not covered here Networking User Interfaces

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Process Management

Manages CPU in terms of running programs, called processes

Schedules processes, picking the next one to get the CPU

Switches between processes, called context switching

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Process-Related Services

Creating processes Terminating processes Changing process parameters (e.g. priority) Providing interprocess communication Providing process synchronization

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Memory Management Assigns areas of memory belonging to

processes to areas of physical memory Manages requests that exceed available

physical memory Controls sharing of memory

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Memory-Related Services Direct allocation requests Direct freeing of memory Serving memory needs implicit in other services Managing sharing of areas of memory

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I/O Device Management Provides common device interface tasks Manages exclusive access Hides device details

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I/O-Related Services Establish access to a device Release a device Read from a device Write to a device Grant exclusive access to a device Provide special device operations

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File System Management Provides translation from names to resources Manages persistent storage of data Presents a device-independent interface Protects resources from unauthorized access

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File System-Related Services Open a file Close a file Read from a file Write to a file Seek within a file Query and modify file parameters

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Security Part of other management responsibilities Authenticates the identity of a requester Authorizes access according to a security policy

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Networking Implements protocol stacks Provides services for:

Establishing connections to remote systems Listening for connections from remote systems Exchanging data with remote systems

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Early OS History No OS on earliest machines Collections of useful routines:

First code reuse Foreshadowed the service provider aspect of

operating systems Machines scheduled with sign-up sheets

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Batch Operating Systems Most CPU time wasted during time slots Separate users from the CPU for more efficient

CPU usage Take programs, run them to completion, and

produce results Trade off efficient CPU usage for loss of user

effectiveness Potentially long time between submitting a job

and getting results

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Time-Sharing Operaing Systems Shorter time slots mean more efficient CPU

usage Take short time slots to the limit Rapidly switch among running programs and

provide multiple user interfaces Useful even with a single user

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Distributed Operating Systems After allowing multiple users and programs,

multiple machines comes next Manage multiple computing systems as a single

pool of computing resources Share file systems Support multiple CPUs cooperating on a single

task

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Key Trends Move away from one user, one program, one

computer-break the triangle of “ones” Make interfaces more uniform Trade off CPU cycles for user convenience:

CPU time gets less expensive Human time gets more expensive

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The Triangle of Ones

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Operating System Structure Monolithic

Kernel structured as a single program Usual design techniques Often criticized

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Operating System Structure (cont.) Layered Design

Dependency on only lower layers Tricky to structure Often requires splitting subsystems into multiple

layers

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Layered Design Example

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Microkernels Move much of the traditional kernel functionality

into separate programs Reduce the size of the kernel Components communicate with messages passed

through the microkernel

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Microkernel Example

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Virtual Machine OS Virtualize the hardware

Create the illusion of multiple machines Each guest believes it has the hardware to itself Allows different OSs to run at the same time

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Virtual Machine Example

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Bootstrapping Load the kernel into memory and transfer

control to it Loaders are like miniOSs

Understand enough memory management to put kernel into memory

Understand enough I/O and file systems to locate kernel and read it into memory

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PC Bootstrapping Sequence BIOS loads Master Boot Record (MBR) from

first block on the disk MBR load first block from active partition Partition boot block:

Some load the kernel directly Some load a secondary loader which loads the

kernel

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System Calls Interface between apps and kernel Looks like a function call in high-level

languages Usually implemented with a software interrupt Processed in a higher-privilege processor mode

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Summary OS roles

Resource manager, service provider, virtual machine

OS responsibilities CPU, memory, I/O devices, file systems, security,

networking Historical evolution

No OS→Batch→Time-sharing→Distributed Increased concurrency at each step

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Summary (cont.) OS organizations

Monolithic, layered, microkernel, virtual machine Bootstrapping

OS-like loaders Locate the kernel, load it, and run it

System Calls Key to service provider role Application/OS interface

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