OPERATING SYSTEMS

Gargi Verma, 13104070

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Index

Software and it’s types Operating System Bootstrap Process Types of OS Components of OS OS Services Examples of OS

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Software

Set of machine-readable instructions that directs a computer's processor to perform specific operations.

Constrasts with computer hardware, which is the physical component of computers.

Includes computer programs, libraries and their associated documentation.

Executable code consists of machine language instructions, consisting of binary numbers, specific to an individual processor – typically a central processing unit (CPU).

Written in a machine language known as machine code or high level programming language or low level assembly language called mnemonics.

High-level languages are translated, using compilation or interpretation or a combination of the two, into machine language. Assembly language is translated into machine code using an assembler.

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Layer Structure of a Computer

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Types based on purpose/domain

Application software: perform special functions or provide entertainment functions to user.

System software: directly operate the computer hardware, to provide basic functionality needed by users and other software, and to provide a platform for running application software. System software includes: Operating systems: essential collections of software that

manage resources and provides common services for other software that runs "on top" of them.

Device drivers: operate or control a particular type of device that is attached to a computer.

Utilities: assist users in maintenance and care of their computers.

Malicious software or malware: developed to harm and disrupt computers. Malware is closely associated with computer-related crimes, though some malicious programs may have been designed as practical jokes.

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Four Components of a Computer System:

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Operating Systems

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. Acts as a general manager supervising the activity of each

component. It’s written in low level language i.e. machine

dependent. When computer is switched on, OS will first load into

the main memory.

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Bootstrap Process The operating system itself is a program that needs to be loaded into the

memory and be run. It is a two-stage process. A very small section of memory is made of ROM and holds a small program

called the bootstrap program. When the computer is turned on, the CPU counter is set to the first instruction

of this bootstrap program and executes the instructions in this program. When loading is done, the program counter is set to the first instruction of the

operating system in RAM.

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Operating systems have gone through a long history of evolution.

TYPES OF OPERATING SYSTEMS

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Batch systems

Designed in the 1950s to control mainframe computers. At that time, computers were large machines that used punched

cards for input, line printers for output and tape drives for secondary storage media.

Each program to be executed was called a job. A programmer who wished to execute a job sends a request to

the operating system. Jobs, together with input data, are fed into the system in a batch. The jobs are then run one after another. No job can be started until previous job is completed

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Multiprogramming System

To use computer system resources efficiently, multiprogramming was introduced.

Resources could be shared between different jobs, with each job being allocated a portion of time to use a resource.

Single user cannot keep CPU and I/O devices busy at all times

Multiprogramming organizes jobs (code and data) so CPU always has one to execute

A subset of total jobs in system is kept in memory

One job selected and run via job scheduling When it has to wait (for I/O for example),

OS switches to another job

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Time sharing systems

Timesharing (multitasking) is logical extension in which CPU switches jobs so frequently that users can interact with each job while it is running, creating interactive computing

Response time should be < 1 second

Each user has at least one program executing in memory process

If several jobs ready to run at the same time CPU scheduling

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Parallel Systems:

When personal computers were introduced, there was a need for an operating system for this new type of computer. During this era, single-user operating systems such as DOS (Disk Operating System) were introduced.

The need for more speed and efficiency led to the design of parallel systems: multiple CPUs on the same machine. Each CPU can be used to serve one program or a part of a program, which means that many tasks can be accomplished in parallel instead of serially. The operating systems required for this are more complex than those that support single CPUs.

Personal Systems:

Distributed Systems:A job that was previously done on one computer can now be shared between computers that may be thousands of miles apart. Distributed systems combine features of the previous generation with new duties such as controlling security.

Real-time systems:A real-time system is expected to do a task within a

specific time constraint. They are used with real-time applications, which monitor, respond to or control external processes or environments.

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COMPONENTS OF OPERATING SYSTEMS

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Operating System Functions

Operating

System

Device configurationControls peripheral devices connected to the computer

File managementTransfers files between main memory and secondary storage, manages file folders, allocates the secondary storage space, and provides file protection and recovery

Memory managementAllocates the use of random access memory (RAM) to requesting processes

Interface platformAllows the computer to run other applications

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Kernel The kernel is a fundamental part of a modern computer's operating

system. The kernel performs its tasks, such as executing processes and

handling interrupts, in kernel space, whereas everything a user normally does, such as writing text in a text editor or running programs in a GUI (graphical user interface), is done in user space to prevent crashing.

The kernel's primary function is to mediate access to the computer's resources, including: The central processing unit: Responsible for running or

executing programs. The kernel takes responsibility for deciding at any time which of the many running programs should be allocated to the processor or processors.

Random-access memory: Store both program instructions and data. The kernel is responsible for deciding which memory each process can use, and determining what to do when not enough is available.

Input/output (I/O) devices: The kernel allocates requests from applications to perform I/O to an appropriate device and provides convenient methods for using the device.

Kernels also usually provide methods for synchronization and communication between processes called inter-process communication (IPC).

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User interface7.17

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.

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Memory manager7.18

One of the responsibilities of a modern computer system is memory management. Although the memory size of computers has increased tremendously in recent years, so has the size of the programs and data to be processed. Memory allocation must be managed to prevent applications from running out of memory. Operating systems can be divided into two broad categories of memory management: monoprogramming and multiprogramming.

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Process manager7.19

A second function of an operating system is process management.

Program, job, and process: A program is a non-active set of instructions stored on disk. A program becomes a job from the moment it is selected for

execution until it has finished running and becomes a program again.

A process is a program in execution. It is a program that has started but has not finished.

To handle multiple processes and jobs, the process manager uses queues (waiting lists).

The whole idea behind process management is to synchronize different processes with different resources.

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Device manager7.20

The device manager, or input/output manager, is responsible for access to input/ output devices. There are limitations on the number and speed of input/output devices in a computer system. The device manager monitors every input/output

deviceconstantly to ensure that the device is functioning properly.

The device manager maintains a queue for each input/output device or one or more queues for similar input/output devices.

The device manager controls the different policies for accessing input/output devices.

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File manager7.21

Operating systems today use a file manager to control access to files. The file manager: controls access to files. supervises the creation, deletion, and

modification of files. controls the naming of files. supervises the storage of files. is responsible for archiving and backups.

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OPERATING SYSTEM SERVICES

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DIFFERENT OPERATING SYSTEMS

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DOS

DOS, short for Disk Operating System, DOS is a single-user, single-tasking operating system with basic kernel functions that are non-reentrant: only one program at a time can use them and DOS itself has no functionality to allow more than one program to execute at a time.

The DOS kernel provides various functions for programs (an application program interface), like character I/O, file management, memory management, program loading and termination.

DOS by default provides a primitive ability for shell scripting, via batch files (with the filename extension .BAT). These are text files that can be created in any text editor. They are executed in the same fashion as compiled programs, and run each line of the batch file as a command. Batch files can also make use of several internal commands, such as GOTO and conditional statements.

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UNIX7.26

UNIX was originally developed in 1969 by Thomson and Ritchie of the Computer Science Research Group at Bell Laboratories.

UNIX is a multiuser, multiprocessing, portable operating systems.

It is designed to facilitate programming, text processing and communication.

They are used heavily for servers in business, as well as workstations in academic and engineering environments. Free UNIX variants, such as Linux, are popular in these areas.

Unix was originally written in assembly language followed by C.

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OS X

OS X (formerly "Mac OS X") is a line of open core graphical operating systems developed, marketed, and sold by Apple Inc..

Unlike its predecessor, OS, OS X is a UNIX operating system. OS X 10.10 "Yosemite", the most recent version, was announced and

released on June 2, 2014.

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LINUX, GNU

The GNU project is a collaboration of many programmers who envisioned to create a free and open operating system that was similar to Unix but with new code licensed on the open-source license model.

It was started in 1983 by Richard Stallman, and is responsible for many components of most Linux variants. Meanwhile, the Linux kernel originated in 1991 as a side project of Linus Torvalds, while a university student in Finland.

Because of its open license model, the Linux kernel code is available for study and modification, which resulted in its use on a wide range of computing machinery from supercomputers to smart-watches.

Linux and GNU have been widely adopted for use in servers and embedded systems such as cell phones.

The Linux kernel is used in some popular distributions, such as Red Hat, Debian, Ubuntu, Linux Mint and Google's Android.

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Microsoft Windows

Microsoft Windows (or simply Windows) is a metafamily of graphical operating systems developed, marketed, and sold by Microsoft.

Microsoft introduced an operating environment named Windows on November 20, 1985 as a graphical operating system shell for MS-DOS in response to the growing interest in graphical user interfaces (GUIs).

The next version of Windows is Windows 10 and is currently available as a technical preview; it is set for release for phones, tablets, laptops, and PCs in late 2015.

Windows is written in C, C++, Assembly. It’s source model is Closed / Shared source.

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Android

Android is a mobile operating system (OS) based on the Linux kernel and currently developed by Google.

With a user interface based on direct manipulation, Android is designed primarily for touchscreen mobile devices such as smartphones and tablet computers, with specialized user interfaces for televisions (Android TV), cars (Android Auto), and wrist watches (Android Wear).

The OS uses touch inputs that loosely correspond to real-world actions, like swiping, tapping, pinching, and reverse pinching to manipulate on-screen objects, and a virtual keyboard.

Android's source code is released by Google under open source licenses and proprietary software.

Android is popular with technology companies which require a ready-made, low-cost and customizable operating system for high-tech devices.

It has been written in C (core), C++, Java.

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Summary

An operating system is the interface between the user and the hardware.

It is loaded by the bootstrap process. It has various types like batch system,

multiprogramming, multitasking, real time, parallel, personal, and distributed.

It has components like the kernel, process manager, file manager, device memory.

GUI is the Graphical User Interface. Linux, UNIX, GNU, Windows, OS X, Android are

some of the examples of an operating system.

Thank you!