Operating System By Prakash G Asnani Assistant Professor Computer Science Government Science College Chikhli

What is operating System ? An operating system (OS) is system software that manages computer hardware and software resources and provides common services for computer programs. OS is software that allows a user to run other applications on a computing device. While it is possible for a software application to interface directly with hardware

Basic functions of operating system Booting: Booting is a process of starting the computer operating system starts the computer to work. Memory Management: Different programs and data execute in memory at one time operating system manages management of memory Loading and Execution A program is loaded in the memory before it can be executed. Operating system provides the facility to load programs in memory easily and then execute it. Data security: Data is an important part of computer system. The operating system protects the data stored on the computer from illegal use, modification or deletion. Disk Management : Operating system manages the disk space. It manages the stored files and folders in a proper way. Process Management: CPU can perform one task at one time. if there are many tasks, operating system decides which task should get the CPU. Device Controlling:operating system also controls all devices attached to computer. The hardware devices are controlled with the help of small software called device drivers.

Types of operating systems Single- and multi-tasking A single-tasking system can only run one program at a time, while a multi- tasking operating system allows more than one program to be running in concurrency. This is achieved by time-sharing, where the available processor time is divided between multiple processes. These processes are each interrupted repeatedly in time slices by a task-scheduling subsystem of the operating system. Multi-tasking may be characterized in preemptive and co-operative types. In preemptive multitasking, the operating system slices the CPU time and dedicates a slot to each of the programs. Distributed A distributed operating system manages a group of distinct computers and makes them appear to be a single computer. The development of networked computers that could be linked and communicate with each other gave rise to distributed computing. Distributed computations are carried out on more than one machine. When computers in a group work in cooperation, they form a distributed system.

Templated In an OS, distributed and cloud computing context, templating refers to creating a single virtual machine image as a guest operating system, then saving it as a tool for multiple running virtual machines. The technique is used both in virtualization and cloud computing management, and is common in large server warehouses. Embedded Embedded operating systems are designed to be used in embedded computer systems. They are designed to operate on small machines like PDAs with less autonomy. They are able to operate with a limited number of resources. They are very compact and extremely efficient by design. Windows CE and Minix 3 are some examples of embedded operating systems. Real-time A real-time operating system is an operating system that guarantees to process events or data by a specific moment in time. A real-time operating system may be single- or multi-tasking, but when multitasking, it uses specialized scheduling algorithms so that a deterministic nature of behavior is achieved. An event-driven system switches between tasks based on their priorities or external events while time-sharing operating systems switch tasks based on clock interrupts.

Library A library operating system is one in which the services that a typical operating system provides, such as networking, are provided in the form of libraries and composed with the application and configuration code to construct a unikernel: a specialized, single address space, machine image that can be deployed to cloud or embedded environments.

Various Flavours of operating system The Windows, OS X, and Linux logos. The Windows GUI. The OS X GUI. Windows 7. Mac OS X Lion. Ubuntu Linux. Apple iOS running on an iPad.

UNIX operating system : case study One of the post powerful and scalable operating system UNIX is the backbone of many data centers including the Internet Big players using UNIX include Sun Microsystems, Apple Inc., Hewlett-Packard and AT&T, which is the original parent company of UNIX Key Features of Unix operating System Unix systems use a centralized operating system kernel which manages system and process activities. All non-kernel software is organized into separate, kernel- managed processes.

Unix systems are preemptively multitasking: multiple processes can run at the same time, or within small time slices and nearly at the same time, and any process can be interrupted and moved out of execution by the kernel. This is known as thread management. Files are stored on disk in a hierarchical file system, with a single top location throughout the system (root, or "/"), with both files and directories, subdirectories, sub-subdirectories, and so on below it. With few exceptions, devices and some types of communications between processes are managed and visible as files or pseudo- files within the file system hierarchy. This is known as everything is a file. However, Linus Torvalds states that this is inaccurate and may be better rephrased as "everything is a stream of bytes"

Features and capabilities of Unix operating system Multitasking and multiuser Programming interface Use of files as abstractions of devices and other objects Built-in networking (TCP/IP is standard) Persistent system service processes called "daemons" and managed by init or inet

Architecture of Unix operating System

Unix Kernal Includes device drivers for computer hardware devices, e.g., graphics cards, network cards, disks A device driver is a program that allows computer programs to interact with hardware devices CPU and memory management File system management Implements system calls that can be used by application programs and system utilities Unix Shells Shells are used for command line input/output to and from users e.g., sh (Bourne shell), bash (Bourne again shell), csh (C shell), ksh(Korn shell) GUIs are used for graphical I/O e.g., Linux KDE, GNOME, Mac OS Leopard

Unix System Utilities System utilities are specialized software tools (commands) e.g., ls, cp, grep, awk, bc, wc, more, rm, mkdir, Daemons provide remote network and administration services e.g., ssh (remote login) lpd (remote printing) httpd (serves web pages) Unix Application Programs This is the software that users commonly interact with e.g., vi and emacs (text editors) gcc (GNU C compiler) javac (Java compiler) java (Java run time virtual machine system)

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