1 Operating System Overview. 2 Today’s Objectives Explain the main purpose of operating systems and describe milestones of OS evolution Explain fundamental

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Operating System Overview

2

Today’s Objectives Explain the main purpose of operating systems and

describe milestones of OS evolution Explain fundamental machine concepts such as:

Instruction processing, Memory hierarchy, Interrupts, and I/O

Explain fundamental OS concepts such as: System calls, processes, synchronization, Files

Explain the POSIX standard (UNIX specification)

3

Today’s Applications

Browser Second LifeYahoo

Chat ClientPop Mail

Application Software

Hardware Network

4

Application Requirements


Chat ClientPop Mail


Hardware Network

Read/w

rite

Display

Print

Store Send/receive

5


Chat ClientPop Mail


Hardware Network

Read/w

rite

Display

Print

StoreRead

/writ

eD

ispla

y

PrintStore

Send/receive

Send/receive


6


Chat ClientPop Mail


Hardware NetworkRead/w

rite

Display

Print

StoreRead

/writ

eD

ispla

y

PrintStore

Send/receive

Send/receiveRead/w

rite

Display

Prin

tSto

re Send/receive


7


Chat ClientPop Mail



rite

Display

Print

StoreRead

/writ

eD

ispla

y

PrintStore

Send/receive

Send/receiveRead/w

rite

Display

Prin

tSto

re Send/receive

Send/re

ceiv

e

Display

Stor

e

Prin

tRead/write


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Delegate Common Functions?


Chat ClientPop Mail



rite

Display

Print

StoreRead

/writ

eD

ispla

y

PrintStore

Send/receive

Send/receiveRead/w

rite

Display

Prin

tSto

re Send/receive

Send/re

ceiv

e

Display

Stor

e

Prin

tRead/write

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Delegate Common Functions to an Operating System

Web Server Second LifeYahooChat

Pop Mail


Operating System

NetworkHardware

Read/WriteStandardOutput

DeviceControl

FileSystem

Communication

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OS Exports a Virtual Machine Interface


Pop Mail


Operating System

NetworkHardware


DeviceControl

FileSystem

Communication

Standard Operating System Interface (Virtual Machine)

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Increase Portability = Minimize Machine-Specific Code


Pop Mail


NetworkHardware

Machine specific part


DeviceControl

FileSystem

Communication

Operating System (machine independent part)


12


Pop Mail


NetworkHardware



DeviceControl

FileSystem

Communication



Port

ab

le

Increase Portability = Minimize Machine-Specific Code

13


Pop Mail



DeviceControl

FileSystem

Communication



Port

ab

le

OS Runs on Multiple Platforms while Presenting same Interface

14


Pop Mail


NetworkHardware



DeviceControl

FileSystem

Communication



Port

ab

le

OS Runs on Multiple Platforms while Presenting same Interface

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POSIX – The UNIX Interface Standard


Pop Mail


NetworkHardware



DeviceControl

FileSystem

Communication


The POSIX Standard Specifies UNIX Interface

Port

ab

le

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A peek into Unix

Application

Portable OS Layer

Libraries

Machine-dependent layer

User space/level

Kernel space/level

• User/kernel modes are supported by hardware

•Some systems do not have clear user-kernel boundary

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Unix: Application

Application (E.g., emacs)

Portable OS Layer

Libraries


Written by programmerCompiled by programmerUses function calls

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Unix: Libraries

Application

Portable OS Layer

Libraries (e.g., stdio.h)


Provided pre-compiledDefined in headersInput to linker (compiler)Invoked like functionsMay be “resolved” when

program is loaded

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Typical Unix OS Structure

Application

Portable OS Layer

Libraries


system calls (read, open..)All “high-level” code

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Typical Unix OS Structure

Application

Portable OS Layer

Libraries


BootstrapSystem initializationInterrupt and exception I/O device driverMemory managementKernel/user mode

switchingProcessor management

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Summary:What is an Operating System?

It is an extended machine Hides the messy details which must be performed Presents user with a virtual machine, easier to use

It is a resource manager Each program gets time with the resource Each program gets space on the resource

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History of Operating Systems

Early systems bring cards to 1401 read cards to tape put tape on 7094 which does computing put tape on 1401 which prints output

Batch Multiprogramming Time sharing Personal

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Structure of a typical job – 2nd generation

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Multiprogramming/timesharing system – three jobs in memory – 3rd generation

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Multiprogramming/timesharing system – three jobs in memory – 3rd generation

Memory Management

Process Management

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History of Computer Generations

First generation 1945 – 1955 vacuum tubes, plug boards

Second generation 1955 - 1965 transistors, batch systems

Third generation 1965 – 1980 ICs and multiprogramming

Fourth generation 1980 – present personal computers

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Computer Hardware Review

Components of a simple personal computerBus

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Large Pentium system

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Components of a simple personal computer

Bus

CPU

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CPU Fetch instruction from code memory Fetch operands from data memory Perform operation (and store result) Go to next instruction

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CPU Registers Fetch instruction from code memory Fetch operands from data memory Perform operation (and store result) Go to next instruction

Note: CPU must maintain certain state Current instructions to fetch (program

counter) Location of code memory segment Location of data memory segment

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CPU Register Examples Hold instruction operands Point to start of

Code segment Data segment Stack segment

Point to current position of Instruction pointer Stack pointer

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CPU Register Examples Hold instruction operands Point to start of

Code segment Data segment Stack segment

Point to current position of Instruction pointer Stack pointer

Why stack?

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Code Layout for Process

Processes have three segments: text, data, stack

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Code Layout for Process

Processes have three segments: text, data, stack

Where is this stored?

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BusCPU Memory

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Memory Hierarchy

Typical memory hierarchy– numbers shown are rough approximations

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BusCPU Memory

I/ODevices

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I/O Interrupt Mechanism

(a)

a) Steps in starting an I/O device and getting interrupt

b) How the CPU is interrupted

(b)

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Computer Hardware ReviewExample I/O Device: Disk

Structure of a disk drive

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Operating System Review:Processes

A process tree A created two child processes, B and C B created three child processes, D, E, and F

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Context Switching

How would you switch CPU execution from one process to another?

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Semaphores

Control access to resources

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Shared Resources, Conflicts, and Deadlocks

(a) A potential deadlock. (b) an actual deadlock.

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Inter-process Communication

Two processes connected by a pipe

Documents

1 Operating System Overview. 2 Today’s Objectives Explain the main purpose of operating systems and describe milestones of OS evolution Explain fundamental