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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 Concepts Operating System Revisited USER FILE MANAGEMENT DISK MANAGEMENT MEMORY MANAGEMENT KERNEL File system and directory implementation, access methods etc. I/O , Disk Scheduling etc. Swapping, Paging, Segmentation, Demand Paging, Page replacement, Trashing etc. Threads, Processes, IPC, Synchronization, CPU Scheduling, Deadlocks 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). Operating System Concepts Abstract View of System Components Operating System Concepts 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). Operating System Concepts 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 Operating System Concepts Memory Layout for a Simple Batch System Operating System Concepts Multiprogrammed Batch Systems Several jobs are kept in main memory at the same time, and the CPU is multiplexed among them. Operating System Concepts 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. Operating System Concepts 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. Operating System Concepts 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) Operating System Concepts 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 Operating System Concepts 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 Operating System Concepts Symmetric Multiprocessing Architecture Operating System Concepts Distributed Systems Operating System Concepts Distributed Systems (cont) • Requires networking infrastructure. • Local area networks (LAN) or Wide area networks (WAN) • May be either client-server or peer-topeer systems. Operating System Concepts General Structure of Client-Server Operating System Concepts 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. Operating System Concepts 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. Operating System Concepts Real-Time Systems (Cont.) • Hard real-time: – Secondary storage limited or absent, data stored in short term memory, or readonly memory (ROM) – Conflicts with time-sharing systems, not supported by general-purpose operating systems. • Soft real-time – Limited utility in industrial control of Operating System Concepts Handheld Systems • Personal Digital Assistants (PDAs) • Cellular telephones • Issues: – Limited memory – Slow processors – Small display screens. Operating System Concepts 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 : Android Nokia OS for Handheld Devices : Symbian Apple Mac OS for Handheld Devices : iPhone OS or iOS Windows pocket PC : Windows Mobile 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 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) 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. 1.1 A distributed system organized as middleware. Note that the middleware layer extends over multiple machines. 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 systems over 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 Transparency Description Access Hide differences in data representation and how a resource is accessed. Eg. big endian vs little endian, various file naming conventions etc. Location Hide 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 Relocation Hide 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) Failure Hide the failure and recovery of a resource. For eg. “ Web page unavailable” : Busy web server or server really down ? Persistence Hide whether a (software) resource is in memory or on disk Different forms of transparency in a distributed system. Scalability Problems 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 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 Scaling Techniques (1) Asynchronous comm., replication (hiding comm latencies), distribution, caching 1.4 The difference between letting: a) a server or b) a client check forms as they are being filled 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 Microkernel • 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. • 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. • Other alternative: Use a monolithic kernel, as in Sprite, where kernel provides all service, this is faster, but less flexible. 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.