Eastern Mediterranean University Computer Engineering Department CMPE242 - OPERATING SYSTEMS SPRING , Course Description Instructors: Gr.1. Asst.Prof.Dr. Ahmet Ünveren Gr.2. Assoc. Prof. Alexander Chefranov

Text book: Abraham Silberschatz, Peter Baer Galvin and Greg Gagne:Operating System Concepts with Java, 6th edition, John Wiley & Sons, Inc., ISBN: Operating System Concepts with Java, 6th edition Reference books: Andrew S. Tanenbaum, Modern Operating Systems, Second Edition, Prentice Hall, H. M. Dietel, P. J. Dietel, and D. R. Choffnes: Operating Systems, 3rd Edition, Pearson Education, ISBN: Operating Systems, 3rd Edition Grading policy: Midterm exam 40% Final exam50% Assignments and Tutorial 5% Lecture Attendance5%

Chapter 1: Introduction What is an Operating System? Mainframe Systems Desktop Systems Multiprocessor Systems Distributed Systems Clustered System Real -Time Systems Handheld Systems Computing Environments

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.

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).

Computer System Organization Computer-system operation  One or more CPUs, device controllers connect through common bus providing access to shared memory  Concurrent execution of CPUs and devices competing for memory cycles

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). Kernel Services:  Process Management  Memory Management  File systems  Device drivers  System calls  Interprocess communication  Network protocols

Simple Batch Systems A fairly simple operating system was used. An operator other than user was needed. A card reader was used as input device. CPU is generally idle due to low speeds of mechanical I/O devices compared to those of electronic ones (e.g. slow punch card reader). Processing speed is increased by batching similar jobs together and run them as a group. Automatic job sequencing allows transfer of control from one job to another.

Spooling Jobs are not read directly into memory but onto the disk. Since reading is time consuming, some other jobs can be performed during reading. Overlap I/O of one job with computation of another job. While executing one job, the OS:  Reads next job from card reader into a storage area on the disk (job queue).  Outputs printout of previous job from disk to printer The main goal is reduce CPU idle time

Multiprogrammed Batch Systems Several jobs are kept in main memory at the same time which is known as job pool. The operating system picks one job from memory to execute. When a job has to wait, operating system switches to another job. Eventually, the first job finishes waiting and gets the CPU back.

OS Features Needed for Multiprogramming Memory management – the system must allocate the memory to several jobs. CPU scheduling – the system must choose among several jobs ready to run. The system must know their exact locations in memory Management of devices including allocation.

Time-Sharing Systems–Interactive Computing A time-shared OS uses CPU scheduling and multiprogramming that provides each user a small portion of time. 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). The CPU is switched among multiple processes so frequently that the users may interact with each program during execution. A job swapped in and out of memory to the disk. On-line communication between the user and the system is provided Time-sharing also compensates for low-speed I/O operations such as low-speed keyboard typing.

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: More work is done in the same time period. Increasing processors by n does not mean decreasing operation time by n.  Economical: Shared peripherals and power supplies. Several programs can be run on data on a shared disk  Increased reliability  fail-soft systems. The failure of one processor does not halt the system. The rest continues to do the task  graceful degradation: The ability to continue providing service proportional to the level of surviving hardware.

Parallel Systems (Cont.) Symmetric multiprocessing (SMP)  Each processor runs an identical copy of the operating system which communicates with each other as needed.  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 Distribute the computation among several physical processors referred to as sites, nodes etc. Unlike tightly-coupled parallel systems, these are Loosely coupled systems – each processor has its own local memory; processors communicate with one another through various communications lines, such as high- speed buses or telephone lines. Advantages of distributed systems.  Resources Sharing.  Computation speed up – load sharing  Reliability -  Communications – information exchange

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 Client-Server Computing Dumb terminals supplanted by smart PCs Many systems now servers, responding to requests generated by clients  Compute-server provides an interface to client to request services  File-server provides interface for clients to store and retrieve files

Peer-to-Peer Computing Another model of distributed system P2P does not distinguish clients and servers  Instead all nodes are considered peers  May each act as client, server or both  Node must join P2P network  Registers its service with central lookup service on network, or  Broadcast request for service and respond to requests for service via discovery protocol  Examples include Limewire

Real-Time Systems Used when rigid time requirements exist on the operation of processor or flow of data. Data brought by sensors must be analyzed and corresponding control adjustments must be done in a small time interval. 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.  Guarantees that critical tasks complete on time. 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.