1. Operating Systems 1 K. Salah Module 1.0: Introduction What is an operating system? Multiprogramming Systems Time-Sharing Systems Parallel Systems Distributed Systems Real -Time Systems

2. Operating Systems 2 K. Salah 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

3. Operating Systems 3 K. Salah 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. –One purpose of OS is to hide peculiarities of hardware devices from the user –Make the computer system convenient to use. Use the computer hardware in an efficient manner.

4. Operating Systems 4 K. Salah Why do we need an operating system? User viewpoint -- provide user interface command interpreter, directory structure, utility programs (compilers, editors, filters) Software developer viewpoint -- enhance the bare machine higher-level I/O, structure files, notion of independent processes, improved storage (size, protection) Efficiency viewpoint -- replace a human operator scheduling jobs, storing I/O (files), invoking necessary programs such as compiler Economic viewpoint -- allow concurrent uses and good scheduling of resources So, the goals are to make the system convenient to use (via system calls) and to manage resources efficiently.

5. Operating Systems 5 K. Salah 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).

6. Operating Systems 6 K. Salah Abstract View of System Components

7. Operating Systems 7 K. Salah Brief History of Operating Systems 1940's -- First Computers 1950's -- Batch Processing 1960's – IC invention -> Multiprogramming (timesharing) 1970's -- Minicomputers & Microprocessors Late 1970's, 1980's -- Networking, Distributed Systems, Parallel Systems 1990's and Beyond – PC’s, WWW, Mobile Systems, and hand-held devices (PDAs), pocket PC, iPods, PS/3, Xbox, …

8. Operating Systems 8 K. Salah Why need multiprogramming? I/O Times vs. CPU times 400 MHz Pentium II = 400 million cycles/second 10 cycles/instruction = 40 million instructions/second Read 1 disk block = 20 msec CPU can do (40 x 10 6 ) / 10 3 = 40,000 instructions/msec Thus: In time to read one disk block, CPU can do 20 * 40,000 = 800,000 instructions !!

9. Operating Systems 9 K. Salah Alternating sequence of CPU and I/O bursts

10. Operating Systems 10 K. Salah 1960’s -- Multiprogramming and Timesharing Multiprogramming: CPU is multiplexed (shared) among a number of jobs -- while one job waiting for I/O, another can use CPU. Advantages: –CPU is kept busy. Disadvantages: –Hardware and O.S. became significantly more complex for handling and scheduling multiple jobs. Timesharing: switch CPU among jobs for pre-defined time interval. Most O.S. issues arise from trying to support multiprogramming -- CPU scheduling, deadlock, protection, memory management, virtual memory, etc.

11. Operating Systems 11 K. Salah Parallel Systems Multiprocessor systems with more than one 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 or fault-tolerant –The ability to continue providing service proportional to the level of surviving hardware.

12. Operating Systems 12 K. Salah Parallel Systems (Cont.) Symmetric multiprocessing (SMP) –Each processor runs an 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 allocates work to slave processors. –More common in extremely large systems –Also used in PS/3 and Sbox  PS/3 has 8 CPUs with one CPU acting as a master

13. Operating Systems 13 K. Salah Symmetric Multiprocessing Architecture

14. Operating Systems 14 K. Salah Distributed Systems Distribute the computation among several physical processors. Loosely coupled system – 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. –Resource sharing  sharing and printing files at remote sites  processing information in a distributed database  using remote specialized hardware devices –Computation speedup – load sharing –Reliability – detect and recover from site failure, function transfer, reintegrate failed site –Communication – message passing

15. Operating Systems 15 K. Salah 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. Hard real-time system. Deadline support –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. –Examples: QNX, FreeRTOS, eCos, EROS, ChorusOS, pSOS Soft real-time system. No deadline support –Limited utility in industrial control or robotics –Useful in applications (multimedia, virtual reality) requiring advanced operating-system features. –Examples: Linux Kurt, VxWorks, Windows CE

16. Operating Systems 16 K. Salah Network vs. Distributed OS Network OS –A configuration in which there is a network of application machines, typically a workstations with multiple server machines. –Server machines can be file servers, printer servers, mail, etc. –Each computer has its own OS. The user must be aware that there are multiple independent machine and must deal with them explicitly. –NW OS allows machines to interact with each other by having a common communication architecture. Distributed OS –A common OS shared by a network of computers –Offers the illusion of a unified system image, i.e. single system image  i.e, a pool of interconnected computers appears as a single unified computing resource –can say that these machines have a Single System Image (SSI) [Buyya vol.1, 1999]. –It provides the user with transparent access to the resources of multiple machines –Therefore:  less autonomy between computers  gives the impression there is a single operating system controlling the network. –Research vehicle –Examples: Bell Labs Inferno & Plan 9, Mach, Amobea by Tanenbaum, Chorus by CMU

17. Operating Systems 17 K. Salah Further Reading P2P computing Multimedia systems Cluster computing Blade servers