OSes: 3. OS Structs 1

Operating SystemsOperating Systems

ObjectivesObjectives– summarise OSes from several perspectivessummarise OSes from several perspectives

Certificate Program in Software DevelopmentCSE-TC and CSIM, AITSeptember -- November, 2003

3. OS Structures(Ch. 3, S&G)

OSes: 3. OS Structs 2

ContentsContents

1.1. OS ComponentsOS Components

2.2. OS ServicesOS Services

3.3. System CallsSystem Calls

4.4. System StructureSystem Structure

5.5. Virtual MachinesVirtual Machines

6.6. OS Design and ImplementationOS Design and Implementation

OSes: 3. OS Structs 3

1. OS Components1. OS Components

1.1.1.1. Process/thread ManagementProcess/thread Management

1.2.1.2. Main Memory ManagementMain Memory Management

1.3.1.3. Secondary Storage ManagementSecondary Storage Management

1.4.1.4. I/O System ManagementI/O System Management

1.5.1.5. File ManagementFile Management

1.6.1.6. Protection/SecurityProtection/Security

1.7.1.7. NetworkingNetworking

OSes: 3. OS Structs 4

1.1. Process/thread Mgmt.1.1. Process/thread Mgmt.

Programs are Programs are passivepassive

Processes Processes executeexecute, each with its own , each with its own program counter, but shared resourcesprogram counter, but shared resources

Threads are Threads are light-weightlight-weight processes processes– much simpler state and control much simpler state and control

continued

OSes: 3. OS Structs 5

Management tools:Management tools:– creation/deletioncreation/deletion– suspension/resumptionsuspension/resumption– synchronisationsynchronisation– communicationcommunication– resource allocation/releaseresource allocation/release– deadlock handlingdeadlock handling

OSes: 3. OS Structs 6

1.2. Main Memory Mgmt.1.2. Main Memory Mgmt.

Depends on system and hardware supportDepends on system and hardware support

Track memory usageTrack memory usage

Decide on process schedulingDecide on process scheduling

Allocate/deallocate memory to jobsAllocate/deallocate memory to jobs

OSes: 3. OS Structs 7

1.3. Secondary Storage Mgmt.1.3. Secondary Storage Mgmt.

Storage and retrievalStorage and retrieval

SchedulingScheduling

Free space managementFree space management

Efficient usage is Efficient usage is essentialessential

OSes: 3. OS Structs 8

1.4. I/O System Mgmt.1.4. I/O System Mgmt.

AimAim: hide device peculiarities: hide device peculiarities

Features:Features:– buffering, caching, spoolingbuffering, caching, spooling– support an abstract interface to devicessupport an abstract interface to devices– support a range of specific devicessupport a range of specific devices

OSes: 3. OS Structs 9

1.5. File Mgmt.1.5. File Mgmt.

Many types of file systems, with different Many types of file systems, with different properties:properties:– speed, capacity, data transfer rate, speed, capacity, data transfer rate,

access method (e.g. sequential, random)access method (e.g. sequential, random)

AimAim: provide a consistent, logical view:: provide a consistent, logical view:– files and directoriesfiles and directories

continued

OSes: 3. OS Structs 10

Features:Features:– creation/deletion of files & directoriescreation/deletion of files & directories– manipulationmanipulation

open, closeopen, close read, write, seekread, write, seek get/set attributesget/set attributes

– mapping to physical storagemapping to physical storage– backup/archivingbackup/archiving

OSes: 3. OS Structs 11

1.6. Protection/Security1.6. Protection/Security

ProtectionProtection: controlling the access of : controlling the access of programs, processes, or users to the programs, processes, or users to the system’s resourcessystem’s resources– e.g. CPU, files, peripherialse.g. CPU, files, peripherials

Network aspects of protection are Network aspects of protection are becoming increasingly importantbecoming increasingly important

OSes: 3. OS Structs 12

1.7. Networking1.7. Networking

Main machine types: Main machine types: – multiprocessor systemsmultiprocessor systems– distributed systemsdistributed systems

Two main communication models:Two main communication models:– message passingmessage passing– shared memoryshared memory

continued

OSes: 3. OS Structs 13

Communication ModelsCommunication Models Fig. 3.5, p.66

process A M

process B M

kernel M

1

2

Message Passing

process A

process B

shared memory

1

2

kernel

Shared memory

OSes: 3. OS Structs 14

2. OS Services2. OS Services

User services:User services:– program execution; I/O operations;program execution; I/O operations;

file manipulation; communication;file manipulation; communication;error detectionerror detection

System efficiency:System efficiency:– resource allocation; accounting;resource allocation; accounting;

protectionprotection

OSes: 3. OS Structs 15

3. System Calls3. System Calls

Process controlProcess control File manipulationFile manipulation Device manipulationDevice manipulation Information maintenanceInformation maintenance CommunicationsCommunications

OSes: 3. OS Structs 16

4. System Structure4. System Structure UNIX (fig. 3.7, p.70)UNIX (fig. 3.7, p.70)

system call interface to kernel

kernel interface to the kernel

signalsterminal handling

character I/O systemterminal drivers

file systemswapping

block I/O systemdisk and tape drivers

CPU schedulingpage replacementdemand pagingvirtual memory

terminal controllersterminals

device controllersdisks and tapes

memory controllersphysical memory

shells and commandscompilers and interpreters

system libraries

USERS

OSes: 3. OS Structs 17

Layered ApproachLayered Approach Fig. 3.8, p.71

layer M-1:hidden

operations

layer M

existingoperations

newoperations :

:

OSes: 3. OS Structs 18

THETHE Layer Structure Layer Structure

layer 5: user programs

layer 4: buffering for I/O devices

layer 3: operator-console device drivers

layer 2: memory management

layer 1: CPU scheduling

layer 0: hardware

OSes: 3. OS Structs 19

5. Virtual Machines5. Virtual Machines

A A virtual machinevirtual machine supplies a set of ‘system’ supplies a set of ‘system’ calls that support a machine in softwarecalls that support a machine in software– it rests on top of the underlying physical it rests on top of the underlying physical

hardwarehardware

A virtual machine A virtual machine may bemay be different from the different from the underlying hardware.underlying hardware.

OSes: 3. OS Structs 20

IssuesIssues

The hardware places limits on the virtual The hardware places limits on the virtual machine’s functionalitymachine’s functionality– e.g. the number/type of peripheralse.g. the number/type of peripherals

How to support virtual user and monitor How to support virtual user and monitor modes in physical user mode?modes in physical user mode?

SpeedSpeed

OSes: 3. OS Structs 21

AdvantagesAdvantages

A virtual machine can protect physical A virtual machine can protect physical system resourcessystem resources

PortabilityPortability

Research/developmentResearch/development

OSes: 3. OS Structs 22

DisadvantagesDisadvantages

Difficult to implement a fast system.Difficult to implement a fast system.

Hard to support modes.Hard to support modes.

Speed issues may require simulation and/or Speed issues may require simulation and/or direct access to the underlying OS or hardwdirect access to the underlying OS or hardware.are.

OSes: 3. OS Structs 23

6. OS Design & Implementation6. OS Design & Implementation

6.1. Design Goals6.1. Design Goals– user and system design goals may conflictuser and system design goals may conflict

– goal tend to be vaguegoal tend to be vague e.g. easy to use, easy to implemente.g. easy to use, easy to implement

OSes: 3. OS Structs 24

6.2. Mechanisms & Policies6.2. Mechanisms & Policies

Separate policy from mechanismSeparate policy from mechanism– policy: what will be donepolicy: what will be done– mechanism: how to do itmechanism: how to do it

ExampleExample: CPU protection: CPU protection– mechanism: timermechanism: timer– policy: timer periodpolicy: timer period

FlexibilityFlexibility Micro-kernels vs. monolithsMicro-kernels vs. monoliths

OSes: 3. OS Structs 25

6.3. Implementation6.3. Implementation

Assembly language vs. high-level Assembly language vs. high-level languageslanguages

ExampleExample: UNIX is coded in C but for : UNIX is coded in C but for ~900 lines of assembler for the scheduler ~900 lines of assembler for the scheduler and device driversand device drivers