Introduction to Os

Chapter No 1
Introduction to Operating System

Introduction

    > A modern computer consists of keyboard, mouse, monitor, main memory, printers and various I/O devices.

    > To manage all this components and using them is challenging job.

    > For this reasons computer are equipped with a layer of software called Operating System, whose job is to provide user programs with a better, simpler, clear, model of computer and to handle all the resources as mentioned above.

Where Operating System fits in?

    > A simple overview of main components of computer can be given as below.

  1. Application Programs

  2. Operating Systems

  3. Hardware

    > The Hardware is at the bottom. It consists of chips, boards, disks, keyboard, monitor and similar physical objects.

    > On the top of the hardware is the Software.

    > Most of the Computers have two modes of operations:

  a. Kernel mode

  b. User Mode

    > The Operating System is the most fundamental piece of software and runs in kernel mode (also called the Supervisor Mode). In this mode it has complete access to all the hardware and can execute any instructions the machine is capable of executing.

    > The rest of the software runs in user mode in which only few machine instructions are available. In particular those instructions which affect control of machine or do I/O are forbidden to user mode programs.

    > For this it can be concluded that Application programs runs in User Mode and Operating System runs in kernel mode.

    > The Operating System runs on bare hardware and provides the base for all the other software.

    > The Operating System differs from user programs in ways other than they reside.

    > In particular they are huge, complex and long lived. They are having huge source code.

    > The Operating System are considered to live a long time as they are very hard to write and having written once is loath to throw it out and start...