advanced operating systems

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Advanced Operating Systems

• Welcome to this course, in Fall Semester 1389-90

• Main TextBooks

1- Tanenbaum’s book

2- Chow’s Book

3- Singhal’s Book

• Other extra references:

1- Attieh’s book

2- Lynch’s book

OS2-Sharif University of Technology - Sem1-90-91; R. Jalili

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Advanced Operating Systems

• Assistants: to be announced.

• Evaluation:

– Mid-Term Exam

– Project

– Review Paper

– Final Exam

• The course Home page and Mailing-list …

• Office Hours: Sunday and Tuesday 8 - 9


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1Introduction to Distributed

Systems and Distributed

Operating Systems (DOSs)(From Tanenbaum’s Book)


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Definition of a Distributed System (1)

A distributed system is:

A collection of independent computers that appears to its

users as a single coherent system.


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Definition of a Distributed System (2)

A distributed system organized as middleware.

Note that the middleware layer extends over multiple machines.

1.1

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Goals in DSs

• Connecting Users and Resources

• Transparency

• Openness

• Scalability

Will be discussed in the next slides.


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Transparency in Distributed Systems

Different forms of transparency in a distributed system.

Transparency Description

AccessHide differences in data representation and how a resource is accessed

Location Hide where a resource is located

Migration Hide that a resource may move to another location

RelocationHide that a resource may be moved to another location while in use

ReplicationHide that a resource may be shared by several competitive users

ConcurrencyHide that a resource may be shared by several competitive users

Failure Hide the failure and recovery of a resource

PersistenceHide whether a (software) resource is in memory or on disk

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Degree of Transparency

• Is transparency good anytime and everywhere?

• Tradeoff between transparency and performance.

- Updating a replicated database!


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Openness

• Offering services based on standards.

• Services are specified through interfaces,

described in IDL (Interface Definition Language)

• Interoperability: two implementations of a system

to co-exist and work together; or

multiple systems developed by different vendors

to be able to work with each other.

• Portability: An application developed to work on

A can be executed on another system B.

• Separating policy from mechanismOS2-Sharif University of Technology - Sem1-89-90; R. Jalili

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Scalability

• Definition of an scalable system?

• 3 different dimensions

– Size: Adding more users and resources to the system.

– Geography: Users and resources can lie far apart.

– Administration: Many administration organization!


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Scalability Obstacles

Examples of scalability limitations.

Concept Example

Centralized services A single server for all users

Centralized data A single on-line telephone book

Centralized algorithms Doing routing based on complete information

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Scalability Solutions

1. Hiding communication latencies: try to avoid waiting

for responses to remote service requests � Use

Asynchronous Communication

• Many applications cannot run on an asynch communication

system

• Next slide example.

2. Distribution: DNS as example

3. Replication: Caching and consistency!


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Scaling Techniques (1)

1.4

The difference between letting:

a) a server or

b) a client check forms as they are being filled

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Scaling Techniques (2)

1.5

An example of dividing the DNS name space into zones.

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Hardware Concepts

1.6

Different basic organizations and memories in distributed computer

systems

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Multiprocessors

A bus-based multiprocessor.

1.7

• Memory is Coherent.

• The bus is overloaded.

• Caching: hit-rate?

• Scalability?


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Software Concepts

An overview of

• DOS (Distributed Operating Systems)

• NOS (Network Operating Systems)

• Middleware

System Description Main Goal

DOSTightly-coupled operating system for multi-processors and homogeneous multicomputers

Hide and manage hardware resources

NOSLoosely-coupled operating system for heterogeneous multicomputers (LAN and WAN)

Offer local services to remote clients

MiddlewareAdditional layer atop of NOS implementing general-purpose services

Provide distribution transparency


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Uniprocessor Operating Systems

Separating applications from operating

system code through

a microkernel.1.11


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Multiprocessor Operating Systems (1)

A monitor to protect an integer against concurrent access.

monitor Counter {

private:

int count = 0;

public:

int value() { return count;}

void incr () { count = count + 1;}

void decr() { count = count – 1;}

}


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Multiprocessor Operating Systems (2)A monitor to protect an integer against concurrent access, but

blocking a process.

monitor Counter {

private:

int count = 0;

int blocked_procs = 0;

condition unblocked;

public:

int value () { return count;}

void incr () {

if (blocked_procs == 0)

count = count + 1;

else

signal (unblocked);

}

void decr() {

if (count ==0) {

blocked_procs = blocked_procs + 1;

wait (unblocked);

blocked_procs = blocked_procs – 1;

}

else

count = count – 1;

}

}


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Multicomputer Operating Systems (1)

General structure of a multicomputer operating system

Message Passing

1.14


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Distributed Shared Memory Systems (1)

a) Pages of address

space distributed

among four

machines

b) Situation after CPU

1 references page 10

c) Situation if page 10

is read only and

replication is used


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DSM – An Interesting Scenario!

False sharing of a page between two independent processes.

1.18

False Sharing!


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Network Operating System (1)

General structure of a network operating system.

1-19


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Network Operating System (2)

Two clients and a server in a network operating system.

1-20


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Network Operating System (3)Different clients may mount the servers in different places.

1.21


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Positioning Middleware

General structure of a distributed system as middleware.

1-22


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Middleware and Openness

In an open middleware-based distributed system, the protocols used by each middleware layer should be the same, as well as the interfaces they offer to applications.

1.23


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Comparison between Systems

Item

Distributed OSNetwork

OSMiddleware-

based OSMultiproc. Multicomp.

Degree of transparency Very High High Low High

Same OS on all nodes Yes Yes No No

Number of copies of OS 1 N N N

Basis for communicationShared memory

Messages Files Model specific

Resource managementGlobal, central

Global, distributed

Per node Per node

Scalability No Moderately Yes Varies

Openness Closed Closed Open Open


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Clients and Servers

General interaction between a client and a server.

1.25


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An Example Client and Server (1)The header.h file used by the client and server.


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An Example Client and Server (2)

A sample server.


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An Example Client and Server (3)

A client using the server to copy a file.

1-27 b


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Application Layering:Processing LevelThe general organization of an Internet

search engine into three different layers

1-28


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Multitiered Architectures (1)

Alternative client-server organizations (a) – (e).

1-29


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Multitiered Architectures (2)

An example of a server acting as a client.

1-30


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Modern Architectures

An example of horizontal distribution of a Web service.

1-31


advanced operating systems

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