Operating System - Introduction of Operating System -Lecture 1

Chapter 1

Introduction

What is an Operating System?
An operating system acts as an intermediary between the user of a computer and the computer hardware. The purpose of an operating system is to provide an environment in which a user can execute programs in a convenient (suitable) and efficient manner.
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.
Computer System Components
1. Hardware – provides basic computing resources (CPU, memory, I/O devices).
2. Operating system – controls and coordinates the use of the hardware among the various application programs for the various users.
3. Applications programs – define the ways in which the system resources are used to solve the computing problems of the users (compilers, database systems, video games, business programs).
4. Users (people, machines, other computers).
Abstract View of System Components
A computer system can be divided roughly into four components: the hardware, the operating system, the application programs, and the users.






Operating System Functions
? Resource allocator – manages and allocates resources.
? Control program – controls the execution of user programs and operations of I/O devices.
? Kernel – the one program running at all times (all else being application programs).
(The kernel is a computer program that is the core of a computer s operating system, with complete control over everything in the system) it is one of the first programs loaded on start-up (after the bootloader). It handles the rest of start-up as well as input/output requests from software, translating them into data-processing instructions for the central processing unit. It handles memory and peripherals like keyboards, monitors, printers, and speakers.
Computer-System Operation
A modern general-purpose computer system consists of one or more CPUs and a number of device controllers connected through a common bus that provides access to shared memory (Figure 1.2). Each device controller is in charge of a specific type of device (for example, disk drives, audio devices, or video displays). The CPU and the device controllers can execute in parallel, competing for memory cycles. To ensure orderly access to the shared memory, a memory controller synchronizes access to the memory.
For a computer to start running—for instance, when it is powered up or rebooted—it needs to have an initial program to run. This initial program, or bootstrap program, Typically, it is stored within the computer hardware in read-only memory (ROM) or electrically erasable programmable read-only memory (EEPROM), known by the general term firmware. It initializes all aspects of the system, from CPU registers to device controllers to memory contents. The bootstrap program must know how to load the operating system and how to start executing that system. To accomplish this goal, the bootstrap program must locate the operating-system kernel and load it into memory.