Introduction to Operating System

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Gillian Glenn
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1 Introduction to Operating System An operating system is a program which manages all the computer hardware. It provides the base for application program and acts as an intermediary between a user and the computer hardware. The operating system has two objectives such as: Firstly, an operating system controls the computer s hardware. The second objective is to provide an interactive interface to the user and interpret commands so that it can communicate with the hardware. The operating system is very important part of almost every computer system. Historical Background By the late 1950s Operating systems were well improved and started supporting following usages : It was able to Single stream batch processing It could use Common, standardized, input/output routines for device access Program transition capabilities to reduce the overhead of starting a new job was added Error recovery to clean up after a job terminated abnormally was added. Job control languages that allowed users to specify the job definition and resource requirements were made possible. After 80 s evolution- August 12, 1981: IBM introduces the IBM PC 1983 Microsoft begins work on MS-Windows 1984 Apple Macintosh comes out 1990 Microsoft Windows 3.0 comes out 1991 GNU/Linux 1992 The first Windows virus comes out

1993 Windows NT 2007: ios 2008: Android OS Basic Services provided by OS It boots the computer It performs basic computer tasks e.g. managing the various peripheral devices e.g. mouse, keyboard It provides a user interface, e.

2 1993 Windows NT 2007: ios 2008: Android OS Basic Services provided by OS It boots the computer It performs basic computer tasks e.g. managing the various peripheral devices e.g. mouse, keyboard It provides a user interface, e.g. command line, graphical user interface (GUI) It handles system resources such as computer's memory and sharing of the central processing unit(cpu) time by various applications or peripheral devices. It provides file management which refers to the way that the operating system manipulates, stores, retrieves and saves data. Error Handling is done by the operating system. It takes preventive measures whenever required to avoid errors. Some popular Operating Systems include Linux, Windows, OS X, VMS, OS/400, AIX, z/os, etc.

3 What OS does? Memory Management Processor Management Device/ Resource Allocation File Management Security Control over system performance Job accounting Error detecting aids Coordination between other software and users Memory Management Keeps tracks of primary memory, i.e., what part of it are in use by whom, what part are not in use.

4 In multiprogramming, the OS decides which process will get memory when and how much. Allocates the memory when a process requests it to do so. De-allocates the memory when a process no longer needs it or has been terminated. Processor Management Keeps tracks of processor and status of process. The program responsible for this task is known as traffic controller. Allocates the processor (CPU) to a process. De-allocates processor when a process is no longer required. Device/ Resource Allocation An Operating System manages device communication via their respective drivers. It does the following activities for device management Keeps tracks of all devices. Program responsible for this task is known as the I/O controller. Decides which process gets the device when and for how much time. Allocates the device in the efficient way. De-allocates devices. Resources are of two types- 1- Sharable 2- Non- sharable OS takes care of both types of resources and allocate them accordingly. File Management

5 A file system is normally organized into directories for easy navigation and usage. These directories may contain files and other directions. An Operating System does the following activities for file management Keeps track of information, location, uses, status etc. The collective facilities are often known as file system. Decides who gets the resources. Allocates the resources. De-allocates the resources. Types of Operating Systems Following are some of the most widely used types of Operating system. Batch Operating System Multiprogramming Operating System Multitasking Operating System Multiprocessor Operating System Distributed Operating System Realtime Operating System Batch OS In this type of system, there is no direct interaction between user and the computer. The user has to submit a job (written on cards or tape) to a computer operator. Then computer operator places a batch of several jobs on an input device. Jobs are batched together by type of languages and requirement. Then a special program, the monitor, manages the execution of each program in the batch.

6 The monitor is always in the main memory and available for execution. Following are some disadvantages of this type of System: No interaction between user and computer. No mechanism to prioritise the processes. Throughput less. CPU is often idle, because the speed of the mechanical I/O devices is slower than the CPU. Multiprogramming Operating System In this the operating system picks up and begins to execute one of the jobs from memory. Once this job needs an I/O operation operating system switches to another job (CPU and OS always busy). Jobs in the memory are always less than the number of jobs on disk(job Pool). If several jobs are ready to run at the same time, then the system chooses which one to run through the process of CPU Scheduling. In Non-multiprogrammed system, there are moments when CPU sits idle and does not do any work. In Multiprogramming system, CPU will never be idle and keeps on processing. Multitasking Operating System Multiprogramming Operating System + preemption = Multitasking OS Time-Sharing Systems are very similar to Multiprogramming batch systems. In fact time sharing systems are an extension of multiprogramming systems. In time sharing systems the prime focus is on minimizing the response time, while in multiprogramming the prime focus is to maximize the CPU usage.

7 MULTIPROCESSOR SYSTEMS A multiprocessor system consists of several processors that share a common physical memory. Multiprocessor system provides higher computing power and speed. In multiprocessor system all processors operate under single operating system. Multiplicity of the processors and how they do act together are transparent to the others. Advantages of Timesharing operating systems are as follows Provides the advantage of quick response. Avoids duplication of software. Reduces CPU idle time. Disadvantages of Time-sharing operating systems are as follows Problem of reliability. Question of security and integrity of user programs and data. Problem of data communication. Distributed operating System Distributed systems use multiple central processors to serve multiple real-time applications and multiple users. Data processing jobs are distributed among the processors accordingly. The processors communicate with one another through various communication lines (such as high-speed buses or telephone lines). These are referred as loosely coupled systems or distributed systems. Processors in a distributed system may vary in size and function. These processors are referred as sites, nodes, computers, and so on. The advantages of distributed systems are as follows With resource sharing facility, a user at one site may be able to use the resources available at another.

8 Speedup the exchange of data with one another via electronic mail. If one site fails in a distributed system, the remaining sites can potentially continue operating. Better service to the customers. Reduction of the load on the host computer. Reduction of delays in data processing. Network operating System A Network Operating System runs on a server and provides the server the capability to manage data, users, groups, security, applications, and other networking functions. The primary purpose of the network operating system is to allow shared file and printer access among multiple computers in a network, typically a local area network (LAN), a private network or to other networks. Examples of network operating systems include Microsoft Windows Server 2003, Microsoft Windows Server 2008, UNIX, Linux, Mac OS X, Novell NetWare, and BSD. The advantages of network operating systems are as follows Centralized servers are highly stable. Security is server managed. Upgrades to new technologies and hardware can be easily integrated into the system. Remote access to servers is possible from different locations and types of systems. The disadvantages of network operating systems are as follows High cost of buying and running a server. Dependency on a central location for most operations. Regular maintenance and updates are required.

9 Real Time operating System A real-time system is defined as a data processing system in which the time interval required to process and respond to inputs is so small that it controls the environment. The time taken by the system to respond to an input and display of required updated information is termed as the response time. So in this method, the response time is very less as compared to online processing. Real-time systems are used when there are rigid time requirements on the operation of a processor or the flow of data and real-time systems can be used as a control device in a dedicated application. A real-time operating system must have welldefined, fixed time constraints, otherwise the system will fail. For example, Scientific experiments, medical imaging systems, industrial control systems, weapon systems, robots, air traffic control systems, etc. There are two types of real-time operating systems. Hard real-time systems Hard real-time systems guarantee that critical tasks complete on time. In hard realtime systems, secondary storage is limited or missing and the data is stored in ROM. In these systems, virtual memory is almost never found. Soft real-time systems Soft real-time systems are less restrictive. A critical real-time task gets priority over other tasks and retains the priority until it completes. Soft real-time systems have limited utility than hard real-time systems. For example, multimedia, virtual reality, Advanced Scientific Projects like undersea exploration and planetary rovers, etc.

Some popular Operating Systems include Linux Operating System, Windows Operating System, VMS, OS/400, AIX, z/os, etc.

Some popular Operating Systems include Linux Operating System, Windows Operating System, VMS, OS/400, AIX, z/os, etc. An Operating System (OS) is an interface between computer user and computer hardware. An operating system is software which performs all the basic tasks like file management, memory management, process