Chapter – 5 Introduction to Operating System

A modern computer system has a variety of resources like the CPU, memory, secondary storage, network, peripheral devices, etc.

A computer without any kind of software for above operations is a practically unusable device, because it may not even have the basic user interface to interact with the user.

Thus an operating system exists to satisfy all these needs. Because it controls the whole system, it is always the first program to be started when the computer system is turned on.

What is an Operating System ?
An operating system is the controller, resource allocator and common services provider for a computer system. Like the government, it performs these functions to ensure smooth and mostly trouble-free operation of the computer.
The Startup Process of a Computer When the computer is supplied power and turned on, the CPU takes control of the whole system.
The computer has a type of permanent memory called ROM (on personal computers, this is often called ROM BIOS (Basic Input Output System or simply BIOS) that contains an initial program. This initial program, called POST (Power On Self Test), performs a basic check on all other components and peripheral devices in the computer and initializes them so they are ready for use.
Once the operating system starts its execution, it takes control of the entire computer system. This entire process is called “booting” the computer to a particular operating system.
Handling Multiprocessor Systems :- A computer system may have more than one CPU (processor) as well. A computer system having more than one processor is known as a multiprocessor system
Starting and Stopping Program Execution When the computer starts, initially it runs only the operating system. The operating system takes complete control of the computer system. It also runs a special program called the shell. The shell provides the user a user interface (UI) to work with. The user interface allows the user to indicate what they want to do.
Providing Security When multiple users are accessing the same computer system, the operating system must provide some level of isolation between the users so that one user cannot disturb the work of another user
The shell is the most visible component of an operating system bundle; so much so that most people identify the operating system by the looks of the shell.
There are two main categories of user interfaces – a Command Line Interface (CLI) and a Graphical User Interface (GUI). The CLI expects only a low-cost low-power text-based terminal.
Supercomputers :-
The largest and the most powerful computers ever built are known as supercomputers. These are computers that can perform millions of billions of floating point (real number) operations per second.
Personal Computers The category of computers most familiar to us is that of personal computers. These computers provide a general platform that caters to the widest possible range of uses and also to users with vastly different skill sets.
Smartphones and Tablets Though you may not have realized it yet, a smartphone is also a computer in its own right. Tablet PCs are a hybrid between the smartphones and personal computers. These devices pose unique challenges for operating system designers because they have severe constraints on processing power, memory, energy usage (because higher energy usage would mean the battery would drain out faster) and screen real estate (the screen size is quite small compared to the PC, and yet, most facilities of a PC are expected).
An Operating System for Smartphones: Android We are going to discuss the Ubuntu Linux operating.
A smartphone or a tablet (or phablet) is actually a small computer and functions as a combination of a phone, a Personal Digital Assistant (PDA) providing secretary-like functions (calendar with scheduling, memos and notes, to-do lists, meeting reminders, access to office documents, messaging service or instant email notifications, etc.) and a portable entertainment hub.
What is Android ?
Android is a free and open source operating system for smartphones that is being developed by the Open Handset Alliance, whose most prominent member is Google, Inc. Android uses a slightly modified version of the Linux kernel. It is designed to support a diverse set of devices. Even though the list of devices running Android include watches, phones with small screens and only numeric or qwerty keyboards, touch screen phones, mid-sized phablets (phone + tablet), larger sized tablet computers, TVs and even microwave ovens, the operating system is primarily designed to provide a rich and attractive