CS 134: Operating Systems · CS 134: Operating Systems ... OS X originates when the user...

CS 134:Operating Systems

Definitions, Abstractions, Taxonomies, Early History

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CS 134:Operating Systems

Definitions, Abstractions, Taxonomies, Early History

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Overview

What Is an OS?

History

Hardware

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Overview

What Is an OS?

History

Hardware

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Overview

What Is an OS?

What is an Operating System Anyway?

Class Exercise: Devise three separate definitions. Discuss.

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Class Exercise: Devise three separate definitions. Discuss.

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CS34What Is an OS?


Several slides follow that aren’t onhandout.

What Is an OS?

It’s A Programmer’s Toolkit

Provide useful functionality to programs:I Prevent duplicated workI Promote reuse

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Provide useful functionality to programs:I Prevent duplicated workI Promote reuse

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What Is an OS?

It’s a Control Program

Provide the rules for the how the machine will operate:I Control the operation of the I/O devicesI Ensure smooth running of the machine

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Provide the rules for the how the machine will operate:I Control the operation of the I/O devicesI Ensure smooth running of the machine

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What Is an OS?

It’s an Abstraction Layer

Make the machine “nicer”, easier to program, higher level. . .I Hide some of the idiosyncrasies of the machineI Provide functionality the underlying machine doesn’t have

Hardware

Operating System

Application

User

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Hardware

Operating System

Application

User

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What Is an OS?



Hardware

Operating System

Application

User

The Core Services and Application Services layers and the Carbon and Cocoa applicationenvironments are packaged in umbrella frameworks (described in the chapter “UmbrellaFrameworks” (page 97)). Many public APIs of the kernel environment are exported throughheaders found in /usr/include.

The first part of this chapter, as summarized in the foregoing paragraphs, presents the architectureof Mac OS X as layers of system software. Following this static perspective of Mac OS X is a moredynamic view that traces the progress of a user event through the system. A typical event in MacOS X originates when the user manipulates an input device such as a mouse or a keyboard. Thedevice driver associated with that device, through the I/O Kit, creates a low-level event, puts itin the window server’s event queue, and notifies the window server. The window serverdispatches the event to the appropriate run-loop port of the target process. There the event ispicked up by the Carbon Event Manager and forwarded to the event-handling mechanismappropriate to the application environment. Events can also be asynchronous, such as a networkpacket containing configuration changes.

A Layered Perspective

A common way to look at complex software is to separate out parts of that software into “layers.”Visually depicted, one layer sits on top of another, with the most fundamental layer on the bottom.This kind of diagram suggests the general interfaces and dependencies between the layers ofsoftware. The higher layers of software, which are the closest to actual application code, dependon the layer immediately under them, and that intermediate layer depends on an even lowerlayer.

Mac OS X is reducible to such a perspective. Figure 3-1 (page 40) illustrates the general structureof Mac OS X system software as interdependent layers of libraries, frameworks, and services.

Figure 3-1 Mac OS X as layers of system software

BSDCarbon Cocoa Java(JDK)

BSDClassic

Core Services

Kernel environment

QuickTimeApplication Services

Applicationenvironment

Although this diagram does help clarify the overall architecture, there are dangers in thenecessarily over-simplified view it presents. The Mac OS X services and subsystems that oneapplication uses—and how it uses them—can be very different from those used by anotherapplication, even one of a similar type. Dependencies and interfaces at the different levels canvary from program to program depending on individual requirements and realities.

With that caveat aside, let’s take a guided tour through the layers depicted in this diagram.

40 A Layered Perspective© Apple Computer, Inc. 2003

C H A P T E R 3

System Architecture

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Hardware

Operating System

Application

User

The Core Services and Application Services layers and the Carbon and Cocoa applicationenvironments are packaged in umbrella frameworks (described in the chapter “UmbrellaFrameworks” (page 97)). Many public APIs of the kernel environment are exported throughheaders found in /usr/include.

The first part of this chapter, as summarized in the foregoing paragraphs, presents the architectureof Mac OS X as layers of system software. Following this static perspective of Mac OS X is a moredynamic view that traces the progress of a user event through the system. A typical event in MacOS X originates when the user manipulates an input device such as a mouse or a keyboard. Thedevice driver associated with that device, through the I/O Kit, creates a low-level event, puts itin the window server’s event queue, and notifies the window server. The window serverdispatches the event to the appropriate run-loop port of the target process. There the event ispicked up by the Carbon Event Manager and forwarded to the event-handling mechanismappropriate to the application environment. Events can also be asynchronous, such as a networkpacket containing configuration changes.

A Layered Perspective

A common way to look at complex software is to separate out parts of that software into “layers.”Visually depicted, one layer sits on top of another, with the most fundamental layer on the bottom.This kind of diagram suggests the general interfaces and dependencies between the layers ofsoftware. The higher layers of software, which are the closest to actual application code, dependon the layer immediately under them, and that intermediate layer depends on an even lowerlayer.

Mac OS X is reducible to such a perspective. Figure 3-1 (page 40) illustrates the general structureof Mac OS X system software as interdependent layers of libraries, frameworks, and services.

Figure 3-1 Mac OS X as layers of system software

BSDCarbon Cocoa Java(JDK)

BSDClassic

Core Services

Kernel environment

QuickTimeApplication Services

Applicationenvironment

Although this diagram does help clarify the overall architecture, there are dangers in thenecessarily over-simplified view it presents. The Mac OS X services and subsystems that oneapplication uses—and how it uses them—can be very different from those used by anotherapplication, even one of a similar type. Dependencies and interfaces at the different levels canvary from program to program depending on individual requirements and realities.

With that caveat aside, let’s take a guided tour through the layers depicted in this diagram.

40 A Layered Perspective© Apple Computer, Inc. 2003

C H A P T E R 3

System Architecture

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What Is an OS?

It’s a Virtual Machine

OS provides an environmentThis environment can be seen as a “new machine”. . .

Hardware —Physical machine+ Core OS —Virtual machine

+ OS Libraries —Virtual machine+ OS Utilities —Virtual machine

+ Application —Virtual machine

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OS provides an environmentThis environment can be seen as a “new machine”. . .

Hardware —Physical machine+ Core OS —Virtual machine

+ OS Libraries —Virtual machine+ OS Utilities —Virtual machine

+ Application —Virtual machine

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What Is an OS?

It’s a Protection Layer

Make the machine more robust—less scope for a bug to havedevastating consequences

I OS does everything programs can’t be trusted to doI OS makes programs play nice with others

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Make the machine more robust—less scope for a bug to havedevastating consequences

I OS does everything programs can’t be trusted to doI OS makes programs play nice with others

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What Is an OS?

It’s a Policy Enforcer

OS provides the mechanisms to enforce various policies

Class Exercise: Examples?

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OS provides the mechanisms to enforce various policies

Class Exercise: Examples?

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What Is an OS?

It’s a Resource Manager

The operating system manages physical resources:I ProcessorI MemoryI Storage devicesI Network devices

etc. . .

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etc. . .

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What Is an OS?

It’s a Resource Manager (cont’d.)

The operating system manages virtual resources:I ProcessesI FilesI UsersI Network connectionsI Windows

etc.. . .

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etc.. . .

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What Is an OS?

It’s a Product

Many operating systems are sold by commercial companiesI Market vs. technical considerationsI The operating system is what comes in the box marked

“operating system”

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It’s a Product

Many operating systems are sold by commercial companiesI Market vs. technical considerationsI The operating system is what comes in the box marked

“operating system”

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It’s a Product

What Is an OS?

Fundamental Abstractions

What are the (user-level) abstractions we’d expect to find in amodern OS?

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What are the (user-level) abstractions we’d expect to find in amodern OS?

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What Is an OS?


Include. . .

I System callsI Processes

I ThreadsI Address spaces

I FilesI FilesI DirectoriesI Filesystems

I EventsI AsynchronousI Synchronous

I IPC MechanismsI SemaphoresI MutexesI Condition Variables

I Communications channelsI PipelinesI Network connections

I UsersI (Remote) Hosts

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Include. . .

I System callsI Processes

I ThreadsI Address spaces

I FilesI FilesI DirectoriesI Filesystems

I EventsI AsynchronousI Synchronous

I IPC MechanismsI SemaphoresI MutexesI Condition Variables

I Communications channelsI PipelinesI Network connections

I UsersI (Remote) Hosts

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What Is an OS?


What are the “resources” that an operating system manages?

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What are the “resources” that an operating system manages?

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What Is an OS?



etc.. . .

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etc.. . .

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What Is an OS?



etc.. . .

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etc.. . .

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What Is an OS?

Taxonomy of Computer Systems

Different computer systems ask different things from their OS

Class Exercise: Give some dimensions across which computersystems vary

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Different computer systems ask different things from their OS

Class Exercise: Give some dimensions across which computersystems vary

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What Is an OS?

Partial Taxonomy of Computer Systems

Different computer systems ask different things from their OS:

Special-purpose ↔ General-purposeSingle-user ↔ Multi-user

Non–Resource-sharing ↔ Resource sharingSingle processor ↔ Multiprocessor

Stand alone ↔ NetworkedCentralized ↔ Distributed

Batch ↔ InteractiveDeadline-free ↔ Real-time

Insecure ↔ SecureSymmetric ↔ Asymmetric

Simple ↔ ComplexSmall ↔ Large

Inexpensive ↔ Expensiveetc.

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Different computer systems ask different things from their OS:

Special-purpose ↔ General-purposeSingle-user ↔ Multi-user

Non–Resource-sharing ↔ Resource sharingSingle processor ↔ Multiprocessor

Stand alone ↔ NetworkedCentralized ↔ Distributed

Batch ↔ InteractiveDeadline-free ↔ Real-time

Insecure ↔ SecureSymmetric ↔ Asymmetric

Simple ↔ ComplexSmall ↔ Large

Inexpensive ↔ Expensiveetc.

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History

Early Computers

1950s—large complex machinesI Operated directly from a consoleI Used interactively by a single userI Ran one program at a time (uniprogramming)I Read data from paper tape, punched cards, or toggle

switchesOS? Maybe a library containing code to work the I/O devices wasuseful.

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Early Computers

1950s—large complex machinesI Operated directly from a consoleI Used interactively by a single userI Ran one program at a time (uniprogramming)I Read data from paper tape, punched cards, or toggle

switchesOS? Maybe a library containing code to work the I/O devices wasuseful.

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Early Computers

History

Simple Batch Systems

Provide better use of resources:I Users access computer indirectlyI Programs and input (jobs) taken from a batch queueI Computer has a human operator to feed it jobs

1401 7094 1401

Card reader

Tape drive Input

tapeOutput tape

System tape

Printer

Need to:I Manage the jobs:I Protect the next program from the previous program

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Provide better use of resources:I Users access computer indirectlyI Programs and input (jobs) taken from a batch queueI Computer has a human operator to feed it jobs

1401 7094 1401

Card reader

Tape drive Input

tapeOutput tape

System tape

Printer

Need to:I Manage the jobs:I Protect the next program from the previous program

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History

SPOOLing Batch Systems

Provide better use of resources—buffer input and outputI Read-ahead input from disk/tapeI Write-behind output to disk/tape

Class Exercise: Why does buffering improve performance?Does buffering always improve performance?

(What assumptions are we making?)

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Provide better use of resources—buffer input and outputI Read-ahead input from disk/tapeI Write-behind output to disk/tape

Class Exercise: Why does buffering improve performance?Does buffering always improve performance?

(What assumptions are we making?)

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History

Multiprogrammed Batch Systems

Provide better use of resources—multiplex the processor:I Run multiple independent programs at onceI Switch to another program when running program waits for

I/OMore work for OS. More complex management of

I I/OI MemoryI Processor

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Provide better use of resources—multiplex the processor:I Run multiple independent programs at onceI Switch to another program when running program waits for

I/OMore work for OS. More complex management of

I I/OI MemoryI Processor

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History

Time-Sharing Systems

Provide better environment for users—multiplex the processorbetween users:

I Run multiple independent programs at onceI Switch between users rapidly

I Illusion of having the machine’s full attention

Yet more complexity for OS:

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Provide better environment for users—multiplex the processorbetween users:

I Run multiple independent programs at onceI Switch between users rapidly

I Illusion of having the machine’s full attention

Yet more complexity for OS:

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History

History Repeats Itself

As new, “smaller” hardware appears, it tends to repeat thisevolution

I Mini computersI Personal computersI PDAsI Embedded systems

I Cell phonesI MP3 PlayersI Cameras, etc.

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As new, “smaller” hardware appears, it tends to repeat thisevolution

I Mini computersI Personal computersI PDAsI Embedded systems

I Cell phonesI MP3 PlayersI Cameras, etc.

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Hardware

Computer Hardware

tape drivesprinterdiskdisk

CPUdisk

controllerprinter

controllertape-drivecontroller

memory

memory controller

system bus

on-line

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Computer Hardware

tape drivesprinterdiskdisk

CPUdisk

controllerprinter


memory

memory controller

system bus

on-line

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Computer Hardware

Hardware

Computer Hardware—CPU & Memory

Need to perform computation!

Fetch Instruction

Execute InstructionStart

I Memory contains program instructions and program dataI Processor registers maintain processor state. Registers

include:I General purpose (address & data) registersI Instruction pointer (aka program counter)I Stack pointer(s)I Control and status registers

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Need to perform computation!

Fetch Instruction


I Memory contains program instructions and program dataI Processor registers maintain processor state. Registers

include:I General purpose (address & data) registersI Instruction pointer (aka program counter)I Stack pointer(s)I Control and status registers20

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Hardware

Computer Hardware—I/O Devices

Need to communicate with the world!I I/O devices and CPU execute concurrentlyI Devices have hardware controllers

I Handles devices of a particular device typeI Some level of autonomyI Local buffer

I I/O is from the device to local buffer of controllertape drivesprinterdiskdisk

CPUdisk

controllerprinter


memory

memory controller

system bus

on-line

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Need to communicate with the world!I I/O devices and CPU execute concurrentlyI Devices have hardware controllers

I Handles devices of a particular device typeI Some level of autonomyI Local buffer

I I/O is from the device to local buffer of controllertape drivesprinterdiskdisk

CPUdisk

controllerprinter


memory

memory controller

system bus

on-line

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Hardware

Programmed I/O

After I/O starts, control returns to user program only on I/Ocompletion

I CPU waits until I/O completes.I At most one I/O request is outstanding at a time

I No simultaneous I/O processing

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Programmed I/O

After I/O starts, control returns to user program only on I/Ocompletion

I CPU waits until I/O completes.I At most one I/O request is outstanding at a time

I No simultaneous I/O processing

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Programmed I/O

Hardware

Polled I/O

Polling == Querying the I/O deviceSeparate I/O into two parts:

I InitiationI Polling

Advantages?

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Polled I/O

Polling == Querying the I/O deviceSeparate I/O into two parts:

I InitiationI Polling

Advantages?

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Polled I/O

Hardware

Interrupt-Driven I/O

Separate I/O into two parts:I InitiationI Asynchronous notification

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Separate I/O into two parts:I InitiationI Asynchronous notification

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Hardware

I/O in User-Level Code

User-level code almost always uses “programmed I/O”(e.g. read and write on a file)

Why?

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User-level code almost always uses “programmed I/O”(e.g. read and write on a file)

Why?

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Hardware

Computer Hardware—CPU with Interrupts

CPU needs another feature. . .

Fetch Instruction


InterruptsEnabled?

No

Yes

Interrupt?No

Yes

Save StateJump to Handler

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CPU needs another feature. . .

Fetch Instruction


InterruptsEnabled?

No

Yes

Interrupt?No

Yes

Save StateJump to Handler

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Hardware

Handling an Interrupt

What needs to happen:I Save state

I All registersI Switch stacks?

I Find out what interrupt was. . .I PollingI Vectored interrupts

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What needs to happen:I Save state

I All registersI Switch stacks?

I Find out what interrupt was. . .I PollingI Vectored interrupts

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Hardware

Types of Interrupts

Various typesI Software exception (also called a trap)I TimerI I/OI Hardware failure

A modern operating system is interrupt driven

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Types of Interrupts

Various typesI Software exception (also called a trap)I TimerI I/OI Hardware failure

A modern operating system is interrupt driven

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Types of Interrupts

Hardware

Other Hardware Features

We’ve covered interrupts, but hardware has other cool features,including:

I CachesI Memory managementI Protection

We’ll come back to hardware as we address these topics.

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We’ve covered interrupts, but hardware has other cool features,including:

I CachesI Memory managementI Protection

We’ll come back to hardware as we address these topics.

2012

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CS34Hardware


CS 134: Operating Systems · CS 134: Operating Systems ... OS X originates when the user...

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