Silberschatz, Galvin and Gagne  2002 Modified for CSCI 399, Royden, Operating System Concepts Operating Systems Lecture 1 Introduction Read: Chapter 1

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 399, Royden, Operating System Concepts Course Web Page The course webpage is located at: This page contains useful course information, lecture slides, homework assignments, etc. Refer to it often.

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 399, Royden, Operating System Concepts What is an Operating System? n A program that acts as an intermediary between a user of a computer and the computer hardware. n Operating system goals: F Execute user programs and make solving user problems easier. F Make the computer system convenient to use. F Use the computer hardware in an efficient manner. n There are many variations on how to do this. The operating system design depends on the system and goals for its use.

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 399, Royden, 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  2002 Modified for CSCI 399, Royden, Operating System Concepts Abstract View of System Components

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 399, Royden, Operating System Concepts Goals for An Operating System User View: Ease of use Good performance Resource allocation (if multiple users) System View: Allocate resources (CPU time, Memory space, file storage space, I/O devices). Manage resources in the face of many, potentially conflicting requests. Act as a Control Program: Manage execution of user programs Operate and control I/O devices.

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 399, Royden, Operating System Concepts Competing Goals Goals for an Operating System: 1)Convenience for the user (especially for PC's) 2)Efficient operation (especially with multi-user systems) There may be a trade-off between these goals Evolution of operating systems focused first on efficiency. Much of Operating Systems theory concentrates on optimal use of resources.

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 399, Royden, Operating System Concepts Operating System Definitions n Resource allocator – manages and allocates resources. n Control program – controls the execution of user programs and operations of I/O devices. n Kernel – the one program running at all times (all else being application programs).

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 399, Royden, Operating System Concepts Mainframe Systems--Batch Processing Early computers (mainframes) were large and run from a console I/0 consisted of card readers, line printers, tape drives, etc. Users did not interact directly with the computer: The user submits the job to the operator The operator runs the job on the computer and delivers the output to the user (sometimes days later!). The output consisted of the output of the program plus a dump of the contents of core memory for debugging. Jobs with similar needs were batched together to increase the efficiency of processing. Problem: CPU was often idle. (I/O devices very slow compared to the CPU speed)

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 399, Royden, Operating System Concepts Memory Layout for a Simple Batch System

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 399, Royden, Operating System Concepts Multiprogrammed Batch Systems A single user cannot keep the CPU and I/O busy all the time. Multiprogramming increases the CPU use by having several jobs in memory at once. When one job has to wait (e.g. for I/O) the CPU switches to another job.

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 399, Royden, Operating System Concepts OS Features Needed for Multiprogramming In multiprogramming systems, the operating system must make decisions for the user: n The OS chooses which jobs (in the job pool) are loaded into memory (job scheduling). n The system must allocate the memory to several jobs (memory management). n The system must choose among several jobs ready to run (CPU scheduling). n The system must allocate devices among jobs. n The system must make sure jobs don't affect one another.

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 399, Royden, Operating System Concepts Time-Sharing Systems–Interactive Computing n Time-sharing uses CPU scheduling and multiprogramming to provide each user with a small share of the computing power. n The CPU is multiplexed among several jobs that are kept in memory and on disk n The switches between jobs occur frequently, so that users can interact with each program as it is running. Processes: n A process is a program that is loaded into memory and executing. n A typical process executes for only a short time before finishing or requiring I/O (waiting). n I/O is slow, so the operating system can switch to the program of another user while waiting.

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 399, Royden, Operating System Concepts Desktop Systems n Personal computers – computer system dedicated to a single user. n I/O devices – keyboards, mice, display screens, small printers. n Try to maximize user convenience and responsiveness. n Often individuals have sole use of computer and do not need advanced CPU utilization of protection features. n Can adopt technology developed for larger operating system. n May run several different types of operating systems (Windows, MacOS, UNIX, Linux)

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 399, Royden, Operating System Concepts Parallel Systems n Multiprocessor systems with more than on CPU in close communication. n Tightly coupled system – processors share memory and a clock; communication usually takes place through the shared memory. n Advantages of parallel system: F Increased throughput F Economical F Increased reliability 4 graceful degradation 4 fail-soft systems

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 399, Royden, Operating System Concepts Parallel Systems (Cont.) n Symmetric multiprocessing (SMP) F Each processor runs and identical copy of the operating system. F Many processes can run at once without performance deterioration. F Most modern operating systems support SMP n Asymmetric multiprocessing F Each processor is assigned a specific task; master processor schedules and allocated work to slave processors. F More common in extremely large systems

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 399, Royden, Operating System Concepts Symmetric Multiprocessing Architecture

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 399, Royden, Operating System Concepts Migration of Operating-System Concepts and Features