McGraw-Hill©The McGraw-Hill Companies, Inc., 2000 OS 1

Operating system is a system that provides interface between hardware and user. Os is a software. Os is system software. 7.2

7.3 A computer is a system composed of two major components: hardware and software. Computer hardware is the physical equipment. Software is the collection of programs that allows the hardware to do its job. Computer software is divided into two broad categories: the operating system and application programs (Figure 7.1). Application programs use the computer hardware to solve users’ problems. The operating system, on the other hand, controls the access to hardware by users.

7.4 Figure 7.1 A computer system

INTRODUCTION An operating system is complex, so it is difficult to give a simple universal definition. Instead, here are some common definitions:  An operating system is an interface between the hardware of a computer and the user (programs or humans).  An operating system is a program (or a set of programs) that facilitates the execution of other programs.  An operating system acts as a general manager supervising the activity of each component in the computer system.

7.6 An operating system is an interface between the hardware of a computer and the user (programs or humans) that facilitates the execution of other programs and the access to hardware and software resources. i Two major design goals of an operating system are: ❑ Efficient use of hardware. ❑ Ease of use of resources.

Multitasking - Tasks sharing a common resource (like 1 CPU) In computing, multitasking is a method by which multiple tasks, also known as processes, share common processing resources such as a CPU. With a multitasking OS, such as Windows XP, you can simultaneously run multiple applications. 7.7

Multitasking refers to the ability of the OS to quickly switch between each computing task to give the impression the different applications are executing multiple actions simultaneously. As CPU clock speeds have increased steadily over time, not only do applications run faster, but OSs can switch between applications more quickly. This provides better overall performance. Many actions can happen at once on a computer, and individual applications can run faster. 7.8

Single Core 7.9

Multicore 7.10

Multithreading Multithreading extends the idea of multitasking into applications, so you can subdivide specific operations within a single application into individual threads. Each of the threads can run in parallel. The OS divides processing time not only among different applications, but also among each thread within an application. In a multithreaded National Instruments LabVIEW program, an example application might be divided into four threads - a user interface thread, a data acquisition thread, network communication, and a logging thread. You can prioritize each of these so that they operate independently. Thus, in multithreaded applications, multiple tasks can progress in parallel with other applications that are running on the system. 7.11

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7.13 Time-sharing systems To use computer system resources efficiently, multiprogramming was introduced. The idea is to hold several jobs in memory at a time, and only assign a resource to a job that needs it on the condition that the resource is available. Multiprogramming brought the idea of time sharing: resources could be shared between different jobs, with each job being allocated a portion of time to use a resource. Because a computer is much faster than a human, time sharing is hidden from the user—each user has the impression that the whole system is serving them exclusively.

7.14 User interface Each operating system has a user interface, a program that accepts requests from users (processes) and interprets them for the rest of the operating system. A user interface in some operating systems, such as UNIX, is called a shell. In others, it is called a window to denote that it is menu driven and has a GUI (graphical user interface) component.

7.15 Multiprogramming In multiprogramming, more than one program is in memory at the same time, and they are executed concurrently, with the CPU switching rapidly between the programs. Figure 7.5 Multiprogramming