books recommended: 1.tanenbaum, a. s., “operating systems”, prentice-hall.2001 2.nutt, g.,...

Books Recommended:

1.Tanenbaum, A. S., “Operating Systems”, Prentice-Hall.2001

2.Nutt, G., “Operating Systems”, Addison-Wesley.2004

3.Penumuchu, C.V., “Simple Real-Time Operating System: A Kernel Inside View”, Trafford Publishing. 2007

4.Singhal, M and Shivaratri, N.G., “Advanced Concepts in Operating Systems”, McGraw-Hill.1994

5. George Colouris, Jean Dollimore, Tim Kinderberg, “Distributed Systems: Concepts and Design”, 4th edition, Pearson. 2006

6. Pradeep K. Sinha, “Distributed Operating Systems: Concepts and Design”, Pearson. 2009

7. William Stallings, “Distributed Operating Systems”

8. Dietel and Dietel, “Distributed Operating Systems”

9. Journal and Conference papers

10. Weblinks, Case Studies

Chapter 1: Introduction

• What is an Operating System?• Mainframe Systems• Desktop Systems• Multiprocessor Systems• Distributed Systems • Clustered System• Real -Time Systems• Handheld Systems

Operating System Concepts

What is an Operating System?

• A program that acts as an intermediary between a user of a computer and the computer hardware.

• Operating system goals:– Execute user programs and make solving

user problems easier.– Make the computer system convenient to

use.• Use the computer hardware in an

efficient manner.


Operating System Revisited

KERNEL

MEMORY MANAGEMENT

DISK MANAGEMENT

FILE MANAGEMENT

USER

Threads, Processes, IPC, Synchronization, CPU Scheduling, Deadlocks etc.

Swapping, Paging, Segmentation, Demand Paging, Page replacement, Trashing etc.

I/O , Disk Scheduling etc.

File system and directory implementation, access methods etc.

Threads, Processes, IPC, Synchronization, CPU Scheduling, Deadlocks etc.

I/O , Disk Scheduling etc.

File system and directory implementation, access methods etc.

Computer System Components

1. Hardware – provides basic computing resources (CPU, memory, I/O devices).

2. Operating system – controls and coordinates the use of the hardware among the various application programs for the various users.

3. Applications programs – define the ways in which the system resources are used to solve the computing problems of the users (compilers, database systems, video games, business programs).

4. Users (people, machines, other computers).


Abstract View of System Components


Operating System Definitions

• Resource allocator – manages and allocates resources.

• Control program – controls the execution of user programs and operations of I/O devices .

• Kernel – the one program running at all times (all else being application programs).


Mainframe Systems• Reduce setup time by batching similar jobs• Automatic job sequencing – automatically

transfers control from one job to another. First rudimentary operating system.

• Resident monitor– initial control in monitor – control transfers to job – when job completes control transfers pack to

monitor


Memory Layout for a Simple Batch System


Multiprogrammed Batch Systems


Several jobs are kept in main memory at the same time, and the CPU is multiplexed among them.

OS Features Needed for Multiprogramming

• I/O routine supplied by the system.• Memory management – the system

must allocate the memory to several jobs.

• CPU scheduling – the system must choose among several jobs ready to run.

• Allocation of devices.


Time-Sharing Systems–Interactive Computing

• The CPU is multiplexed among several jobs that are kept in memory and on disk (the CPU is allocated to a job only if the job is in memory).

• A job swapped in and out of memory to the disk.

• On-line communication between the user and the system is provided; when the operating system finishes the execution of one command, it seeks the next “control statement” from the user’s keyboard.

• On-line system must be available for users to access data and code.


Desktop Systems• Personal computers – computer system

dedicated to a single user.• I/O devices – keyboards, mice, display

screens, small printers.• User convenience and responsiveness.• Can adopt technology developed for larger

operating system’ often individuals have sole use of computer and do not need advanced CPU utilization of protection features.

• May run several different types of operating systems (Windows, MacOS, UNIX, Linux)


Parallel Systems• Multiprocessor systems with more than on CPU

in close communication.• Tightly coupled system – processors share

memory and a clock; communication usually takes place through the shared memory.

• Advantages of parallel system: – Increased throughput– Economical – Increased reliability

• graceful degradation• fail-soft systems


Parallel Systems (Cont.)• Symmetric multiprocessing (SMP)

– Each processor runs and identical copy of the operating system.

– Many processes can run at once without performance deterioration.

– Most modern operating systems support SMP• Asymmetric multiprocessing

– Each processor is assigned a specific task; master processor schedules and allocated work to slave processors.

– More common in extremely large systems


Symmetric Multiprocessing Architecture


Distributed Systems


Distributed Systems (cont)• Requires networking infrastructure.• Local area networks (LAN) or Wide

area networks (WAN)• May be either client-server or peer-to-

peer systems.


General Structure of Client-Server


Clustered Systems

• Clustering allows two or more systems to share storage.

• Provides high reliability.• Asymmetric clustering: one server runs the

application while other servers standby.• Symmetric clustering: all N hosts are running

the application.


Real-Time Systems• Often used as a control device in a

dedicated application such as controlling scientific experiments, medical imaging systems, industrial control systems, and some display systems.

• Well-defined fixed-time constraints.• Real-Time systems may be either hard

or soft real-time.


Real-Time Systems (Cont.)

• Hard real-time:– Secondary storage limited or absent, data stored in short

term memory, or read-only memory (ROM)– Conflicts with time-sharing systems, not supported by

general-purpose operating systems.

• Soft real-time– Limited utility in industrial control of robotics– Useful in applications (multimedia, virtual reality)

requiring advanced operating-system features.


Handheld Systems

• Personal Digital Assistants (PDAs)• Cellular telephones• Issues:

– Limited memory– Slow processors– Small display screens.


Similar Issues for

•Distributed OS•Real Time OS•Multimedia OS•Security Aspects•Case studies : Classical and Mobile OS

History of Commercial OS Google OS for Handheld Devices : AndroidNokia OS for Handheld Devices : Symbian

Apple Mac OS for Handheld Devices :

Windows pocket PC : Windows Mobile

iPhone OS or iOS

2009 – 2010 : Microsoft Windows 7, Apple’s Mac “ Snow Leopard”, Google Chrome OS

2006 : Microsoft Windows Vista

2002 - 2004 : Red Hat, Solaris, Debian, Fedora Core, Suse, Ubuntu

1954 : MIT’s OS for UNIVAC 1103

1955 : GM OS for IBM 701

1964 : DOS for IBM Mainframes

1969 : AT&T designed Unix

1977 : Berkley Software Distribution, variant of Unix

1981 : IBM PC ( IBM + Microsoft ) and MS-DOS came up

1983 : Apple Lisa by Apple Inc.

1987 : Microsoft and IBM fall apart .

Microsoft : Graphical OS in 1993 : Windows NT, Windows 95, 98, Me etc. IBM : OS\2

1991 : Linux : Unix like OS Kernel

1996 : Macintosh system and its OS : Mac OS

1995 : Apple buys NeXT (released by Steve, ex-employee of Apple Inc.)

2001 : Apple abandons its OS and introduces Mac OS X ( Nod to X Window and X OS).

Windows responds by releasing Windows XP family

• Distributed Systems vs. Computer Networks

• Distributed System is collection of independent computers that appears to its users as a single coherent system.• A software built on top of computer networks to give it high degree of coherence and transparency• There is a layer on top of operating system called MIDDLEWARE for providing coherence.• Eg. In WWW everything looks like a web document

• In computer Networks, users are exposed to actual machines with different OS and hardware.

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.

2 aspects of the definition:

•Hardware: machines are autonomous

•Software: users think of system as a single computer

Definition of a Distributed System (2)

A distributed system organized as middleware.Note that the middleware layer extends over multiple machines.

1.1

Characteristics : •The difference between various computers and way in which they interact is hidden from users.•Easy to expand and scale.•Continuously available (w.r.t. faults)•MIDDLEWARE to support heterogenous systems.

Examples of Distributed Systems:

• Network of workstations in university :If whole system looks like single processor time sharing system (multi – user).

• Workflow information system that supports automatic processing of order

• WWW : URL based gigantic centralized document system

Advantages of distributed systemsover centralized systems• Economics: microprocessors offer a better price/performance than mainframes• Speed: distributed system may have more total computing power than mainframe.• Inherent distribution: some applications involve spatially separated machines• Reliability: if one machine crashes, the system as a whole can still survive• Incremental growth: Computing power can be added in small increments

Disadvantages of distributed systems

• Software: little software exists for such systems today• Networking: the network can saturate or cause other problems• Security: easy access also applies to secret data

Goals• Connecting users to resources : Eg. web documents, printers, Groupware etc.• Transparency : DS should be able to present its users that it is a single computer system.• Openness : System that offers services according to standard rules that describe syntax and semantics of those services. In DS services specified through interfaces written in Interface Definition Language (IDL) (analogous to protocols in networks) A process needs a certain interface to talk to another process that provides that interface.

Scalability

Transparency in a Distributed System

Different forms of transparency in a distributed system.

Transparency Description

AccessHide differences in data representation and how a resource is accessed. Eg. big endian vs little endian, various file naming conventions etc.

LocationHide where a resource is located. Achieved by assigning logical names in url like www.hotmail.com/home.html

Migration Hide that a resource may move to another location

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

Replication Eg Mobile users with wireless laptops.

Concurrency

Hide that a resource may be shared by several competitive users. Eg. Cooperative sharing (networks) vs. competitive sharing (two users having same file server)

FailureHide the failure and recovery of a resource. For eg. “ Web page unavailable” : Busy web server or server really down ?

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

Scalability Problems

Examples of scalability limitations.

Distributed Algorithm :

1.No m/c has complete information about system state

2.Machines make decisions based on local information

3.Failure of a m/c do not ruin algorithm

4.There is no implicit assumption that clock exists

Concept Example

Centralized services A single server for all users

Centralized data A single on-line telephone book

Centralized algorithmsDoing routing based on complete information

Scaling Techniques (1)

1.4

The difference between letting:

a) a server or

b) a client check forms as they are being filled

Asynchronous comm., replication (hiding comm latencies), distribution, caching

Scaling Techniques (2)

1.5

An example of dividing the DNS name space into zones.

Flexibility

System should provide services in a flexible manner, preferably by using a microkernel, as shown below (Amoeba o/s)

User File Directory Process Server server server

______________ __________________________ Microkernel | microk | microk | microkernel

-------------------------------------------------------------------Network

• The microkernel has a small footprint and only provides basic or minimal services like, ipc, some memory management, low-level scheduling (dispatching) and low level I/O .The microkernel has a small footprint and only provides basic or minimal services like, ipc, some memory management, low-level scheduling (dispatching) and low level I/O .• All other services should be implemented as user level services. All other services should be implemented as user level services. • This makes the system highly modular, with well-defined interfaces to each of the services, so that each service is available to every client, independent of location. This makes the system highly modular, with well-defined interfaces to each of the services, so that each service is available to every client, independent of location. • It also makes it easy to implement, install and debug new services, i.e., without stopping the system or booting a new kernel.It also makes it easy to implement, install and debug new services, i.e., without stopping the system or booting a new kernel.• Other alternative: Use a monolithic kernel, as in Sprite, where kernel provides all service, this is faster, but less flexible.Other alternative: Use a monolithic kernel, as in Sprite, where kernel provides all service, this is faster, but less flexible.

Microkernel

Reliability• issues of availability, consistency, security and fault-tolerance• Availability is the fraction of time the system is usable. This can be enhanced by designing such that it does not require the simultaneous functioning of a substantial number of critical components. Redundancy of key components also

increases availability.• Consistency implies that if file redundancy is there, thus all copies of the file on different servers must have the same data. This is difficult if updates are frequent.• Security must be provided in the form of protection from unauthenticated users and unauthorized usage – more difficult in distributed systems.• Fault-tolerance is to be provided so that when failures occur, they will be transparent to users. A degraded service should still be available if some servers go down.

Performance• Efficient and speedy performance is a major requirement, but difficult to achieve.• Issues of response time, throughput, system utilization and amount of network capacity consumed are important.• Speedup is never N times that of a centralized system, because of the overhead of communication, which is slow due to message passing.

books recommended: 1.tanenbaum, a. s., “operating systems”, prentice-hall.2001 2.nutt, g.,...

Documents