Introduction to Operating Systems

General DefinitionAn OS is a program which acts as an interface between

computer system users and the computer hardware. It provides a user-friendly environment in which a user

may easily develop and execute programs. Otherwise, hardware knowledge would be mandatory

for computer programming. So, it can be said that an OS hides the complexity of

hardware from uninterested users.

In general, a computer system has some resources which may be utilized to solve a problem. They areProcessor(s)MemoryI/OFile System etc.

The OS manages these resources and allocates them to specific programs and users. With the management of the OS, a programmer is rid of difficult hardware considerations. An OS provides services for Processor Management Memory Management Device Management File Management Concurrency Control

For example imagine we are supposed to add two numbers and display it on screen of the monitor.

Without the OS, we would give commands directly to the CPU. That is we would have provide the machine language instructions such as “load number 1 to registry address xoo5, fetch instruction from….”.

This is a tedious job and would take a long time period to finally output the result on screen.

If we had an OS, it would do all these commands behind the scene and quickly output the result on screen.

With the advantage of easier programming provided by the OS, the hardware, its machine language and the OS constitutes a new combination called as a virtual (extended) machine.

Operating Systems

Application Programs

Machine Language

Hardware

User

Virtual Extended Machine

Kernel In computing, the kernel is the main

component of most computer operating systems; it is a bridge between applications and the actual data processing done at the hardware level.

The kernel's responsibilities include managing the system's resources (the communication between hardware and software components).

Usually, as a basic component of an operating system, a kernel can provide the lowest-level abstraction layer for the resources (especially processors and I/O devices) that application software must control to perform its function.

Operating System EvolutionThe first computers used batch operating systems, in which

the computer ran batches of jobs without stop.Programs were punched into cards that were usually copied

to tape for processing. When the computer finished one job, it would immediately start the next one on the tape.

Professional operators, not the users, interacted with the machine.

Users dropped jobs off, then returned to pick up the results after their jobs had run. This was inconvenient for the users, but the expensive computer was kept busy with a steady stream of jobs.

In the 1960s, time-shared operating systems began replacing batch systems.

Users interacted directly with the computer via a printing terminal like the Western Electric Teletype shown here.

Several users shared the computer at the same time, and it spent a fraction of a second on each one's job before moving on to the next.

A fast computer could work on many user's jobs at the same time, while creating the illusion that they were receiving its full attention.

Printing terminals required that programs had character or command-line user interfaces (CLI), in which the user typed responses to prompts or typed commands. The interaction scrolled down a roll of paper.

(Still There was no display units!!)

Printing terminals were later replaced by video terminals that could only display fixed size characters.

Some could be used to create forms on the screen, but many simply scrolled like a "glass Teletype."

Personal computers became affordable in the mid 1970s. The Altair 8800, shown here, was the first commercially viable personal computer marketed to individuals.

Beginning in January 1975, the Altair was sold to hobbyists in kit form. The Altair did not have an operating system, since it had only toggle switches and light-emitting diodes for input and output.

People soon connected terminals and floppy disk drives to Altairs. In 1976, Digital Research introduced the CP/M operating system for the

Altair and computers like it. CP/M and later DOS had CLIs that were similar to those of the time-shared operating systems, but the computer was dedicated to a single user, not shared.

As hardware prices fell, personal computers with bit-mapped displays that could control individual pixels were developed. These made personal computer with graphical user interfaces (GUIs) possible.

The first commercial success was the Apple Macintosh which was introduced in 1984. The initial Macintosh pushed the state of the hardware art, and was restricted to a small, monochrome display.

As hardware continued to evolve, larger, color Macs were developed and Microsoft introduced Windows, their GUI operating system.

The Macintosh operating system was based on decades of research on graphically-oriented personal computer operating systems and applications.

This photo of shows Ivan Sutherland's pioneering program Sketchpad in the early 1960s. Sketchpad foreshadowed many of the characteristics of a modern GUI, but the hardware cost millions of dollars and filled a room.

After many generations of research projects on large computers and improvement in hardware, the Macintosh became economically feasible.

Research prototypes like Sketchpad are still being developed at universities and in research labs. They will form the basis of future products.

DOS eraStands for Disk Operating System.This was a CLI type OS, developed for IBM Corp. in 1981

which was designed to be used as the OS for x86 based (32 bit) computers.

DOS was inspired from the CP/M developed by Digital Research for 8 bit computers in the 1970’s era.

It later became popular when Microsoft bought and licensed it under the name MS-DOS in 1981.

They started to develop more variations of it and sold it with many hardware manufacturers thus making it widely popular.

Windows EraMicrosoft Windows is a series of graphical

interface operating systems developed, marketed, and sold by Microsoft.

This was introduced in 1985 as an add-on to MS-DOS in response to the growing interest in Graphical User Interfaces.

It managed to take over nearly 90% of the market share overtaking the first ever GUI based OS, the Mac OS.

UNIXIt is a multitasking, multi-user computer operating

system originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, Michael Lesk and Joe Ossanna.

The Unix operating system was first developed in assembly language, but by 1973 had been almost entirely recoded in C, greatly facilitating its further development and porting to other hardware.

Today's Unix system evolution is split into various branches, developed over time by AT&T as well as various commercial vendors, universities (such as University of California, Berkeley's BSD), and non-profit organizations.

UNIX cntd…The Open Group, an industry standards consortium, owns

the UNIX trademark. Only systems fully compliant with and certified according

to the Single UNIX Specification are qualified to use the trademark; others might be called Unix system-like or Unix-like, although the Open Group disapproves of this term.

However, the term Unix is often used informally to denote any operating system that closely resembles the trademarked system.

UNIX cntd..Originally, Unix was meant to be a programmer's workbench

more than to be used to run application software. The system grew larger as the operating system started

spreading in the academic circle, as users added their own tools to the system and shared them with colleagues.

Unix was designed to be portable, multi tasking and multi-user in a time-sharing configuration.

Unix operating systems are widely used in servers, workstations, and mobile devices since it is considered to be one of the safest OS’s to be ever built.

LINUXLinux is a Unix-like computer operating system assembled

under the model of free and open source software development and distribution.

The defining component of Linux is the Linux kernel, an operating system kernel first released 5 October 1991 by Linus Torvalds.

Mac OSMac OS is a series of graphical user interface-based operating

systems developed by Apple Inc. for their Macintosh line of computer systems.

The original version was the integral and unnamed system software first introduced in 1984 with the original Macintosh, and referred to simply as the System software.

This is credited with popularizing the graphical user interface concept.

Mac OS releases have existed in two series, Classic Mac OS from 1984 to 2000 and Mac OS X from 2001 to present. Both series share a general interface design, but have very different internal architectures.

The Design Apple deliberately sought to minimize the user's conceptual

awareness of the operating system. This includes tasks which required more operating system knowledge

on other systems would be accomplished by intuitive mouse gestures and simple graphic controls on a Macintosh, making the system more user-friendly and easily mastered.

This would differentiate it from then current systems such as MS-DOS which were more technically challenging to operate.

The core of the system software was held in ROM, with updates provided free of charge by Apple dealers (on floppy disk).

The user's involvement in an upgrade of the operating system was also minimized to running an installer, or simply replacing system files.

This simplicity differentiated the product from others.

Mobile OS’sA mobile operating system, also referred to

as mobile OS, is the operating system that operates a Smartphone, tablet, PDA, or other digital mobile devices.

Modern mobile operating systems combine the features of a personal computer operating system with touchscreen, cellular, Bluetooth, WiFi, GPS mobile navigation, camera, video camera, speech recognition, voice recorder, music player, Near field communication, personal digital assistant (PDA) and other features.

Mobile OS’s Android – Google Inc.Blackberry OS – Blackberry iOS – Apple Inc.Symbian OS– NokiaWindows Phone – MicrosoftUbuntu Phone – UbuntuTizen OS - Samsung

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