Silberschatz, Galvin and Gagne  Operating System Concepts 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

Silberschatz, Galvin and Gagne  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.

Silberschatz, Galvin and Gagne  Operating System Concepts 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).

Silberschatz, Galvin and Gagne  Operating System Concepts Abstract View of System Components

Silberschatz, Galvin and Gagne  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. operating system is Kernel –( the one program running at all times all else being application programs).

Silberschatz, Galvin and Gagne  Operating System Concepts Mainframe Systems (Batch Systems) Early computers were physically enormous machines run from a console. The common input devices were card readers and tape drives. The common output devices were line printers, tape drives, and card punches. The user did not interact directly with the computer systems. Rather, the user prepared a job which consisted of the program, the data, and some control information about the nature of the job (control cards)-and submitted it to the computer operator. The job was usually in the form of punch cards.

Silberschatz, Galvin and Gagne  Operating System Concepts Mainframe Systems (Batch Systems) At some later time( after minutes, hours, or days), the output appeared. The operating system in these early computers was fairly simple. Its major task was to transfer control automatically from one job to the next. To speed up processing, operators batched together jobs with similar needs and ran them through the computer as a group. The output from each job would be sent back to the appropriate programmer.

Silberschatz, Galvin and Gagne  Operating System Concepts Mainframe Systems Reduce setup time by batching(التجميع ) similar jobs Automatic job sequencing – automatically transfers control from one job to another. First rudimentary(بدائي ) operating system. Resident monitor  initial control in monitor  control transfers to job  when job completes control transfers pack to monitor

Silberschatz, Galvin and Gagne  Operating System Concepts Memory Layout for a Simple Batch System

Silberschatz, Galvin and Gagne  Operating System Concepts Mainframe Systems (Multiprogrammed Batch Systems) Several jobs are kept in main memory at the same time, and the CPU is multiplexed among them.

Silberschatz, Galvin and Gagne  Operating System Concepts Mainframe Systems (Multiprogrammed Batch Systems) operating system picks and begins to execute one of the jobs in the memory. Eventually, the job may have to wait for some task, such as an I/O operation to complete. In a non-multiprogrammed system, the CPU would sit idle. In a multiprogramming system, the operating system simply switches to, and executes, another job. When that job needs to wait, the CPU is switched to another job, and so on. Eventually, the first job finishes waiting and gets the CPU back. As long as at least one job needs to execute, the CPU is never idle.

Silberschatz, Galvin and Gagne  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.

Silberschatz, Galvin and Gagne  Operating System Concepts Mainframe Systems (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.

Silberschatz, Galvin and Gagne  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(ملاءمة ) and responsiveness(استجابة ). 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)

Silberschatz, Galvin and Gagne  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: By increasing the number of processors, we hope to get more work done in less time.  Economical : Multiprocessor systems can save more money than multiple single-processor systems, because they can share peripherals, mass storage, and power supplies.  Increased reliability

Silberschatz, Galvin and Gagne  Operating System Concepts Parallel Systems (Increased reliability)  If functions can be distributed properly among several processors, then the failure of one processor will not halt the system, only slow it down. If we have ten processors and one fails, then each of the remaining nine processors must pick up a share of the work of the failed processor. Thus, the entire system runs only 10 percent slower, rather than failing altogether. This ability to continue providing service proportional. to the level of surviving hardware is called graceful degradation. Systems designed for graceful degradation are also called fault tolerant.

Silberschatz, Galvin and Gagne  Operating System Concepts Parallel Systems( Symmetric, asymmetric multiprocessing) The most common multiple-processor systems now use symmetric multiprocessing (SMP), in which each processor runs an identical copy of the operating system, and these copies communicate with one another as needed. Some systems use asymmetric multiprocessing, in which each processor is assigned a specific task. A master processor controls the system; the other processors either look to the master for instruction or have predefined tasks. This scheme defines a master-slave relationship. The master processor schedules and allocates work to the slave processors.

Silberschatz, Galvin and Gagne  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

Silberschatz, Galvin and Gagne  Operating System Concepts Symmetric Multiprocessing Architecture

Silberschatz, Galvin and Gagne  Operating System Concepts 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.  Resources Sharing  Computation speed up – load sharing  Reliability  Communications

Silberschatz, Galvin and Gagne  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-to-peer systems.

Silberschatz, Galvin and Gagne  Operating System Concepts Client-Server Systems Terminals connected to centralized systems are now being supplanted( حل محل ) by PCs. Correspondingly, user-interface functionality that used to be handled directly by the centralized systems is increasingly being handled by the PCs. As a result, centralized systems today act as server systems to satisfy requests generated by client systems.

Silberschatz, Galvin and Gagne  Operating System Concepts General Structure of Client-Server

Silberschatz, Galvin and Gagne  Operating System Concepts Clustered Systems Like parallel systems, clustered systems gather together multiple CPUs to accomplish computational work. Clustered systems differ from parallel systems, however, in that they are composed of two or more individual systems coupled together. The generally accepted definition is that clustered computers share storage and are closely linked via LAN networking.

Silberschatz, Galvin and Gagne  Operating System Concepts Clustered Systems In asymmetric clustering, one machine is in hot standby mode while the other is running the applications. The hot standby host (machine) does nothing but monitor the active server. If that server fails, the hot standby host becomes the active server. In symmetric mode, two or more hosts are running applications, and they are monitoring each other. This mode is obviously more efficient, as it uses all of the available hardware. It does require that more than one application be available to run.

Silberschatz, Galvin and Gagne  Operating System Concepts Clustered Systems( Summary) 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.

Silberschatz, Galvin and Gagne  Operating System Concepts Real-Time Systems A real-time system is used when rigid time requirements have been placed on the operation of a processor or the flow of data; thus, it is 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. A real-time system has well-defined, fixed time constraints. Processing must be done within the defined constraints, or the system will fail.. Real-Time systems may be either hard or soft real-time.

Silberschatz, Galvin and Gagne  Operating System Concepts Hard and Soft real-time systems A hard real-time system guarantees that critical tasks be completed on time. This goal requires that all delays in the system be bounded, from the retrieval of stored data to the time that it takes the operating system to finish any request made of it. A less restrictive type of real-time system is a soft real-time system, where a critical real-time task gets priority over other tasks, and retains that priority until it completes.

Silberschatz, Galvin and Gagne  Operating System Concepts Real-Time Systems (Cont.) Hard real-time:  Secondary storage limited or absent, data stored in short term memory, or read-only memory (ROM) not supported by general- purpose operating systems. Soft real-time  Useful in applications (multimedia, virtual reality) requiring advanced operating-system features.

Silberschatz, Galvin and Gagne  Operating System Concepts Handheld Systems Personal Digital Assistants (PDAs) Cellular telephones Issues:  Limited memory  Slow processors  Small display screens.

Silberschatz, Galvin and Gagne  Operating System Concepts Migration of Operating-System Concepts and Features

Silberschatz, Galvin and Gagne  Operating System Concepts Computing Environments Traditional computing Web-Based Computing Embedded Computing