OPERATING SYSTEM BASICS: Introduction

INTRODUCTION

Every computer system consists of two parts, hardware devices and software routines.

• Hardware devices perform physical operations. Software routines oversee and guide the actions of the hardware. Hardware consists of those parts of the computer that you can touch.
  
• Software is the logical, intangible parts of the computer. The operating system is also software that is designed to control and coordinate all operations that occur in a computer. The operating system acts as an intermediary between other software applications and the hardware, which is required to store and execute the operating system and software applications. In addition, the operating system accepts commands from the user and executes them to perform a desired operation. 

There are thousands of different operating systems that you can use with microcomputers. The complexity of each operating system depends on the application that the microcomputer is designed to execute. In personal computers, there are two basic types of operating systems:

1.  Single-process systems: Systems that can perform only one task at a time
2.  Multiple-process systems: Systems that can perform several tasks at a time

In a single-process system, the operating system executes only a single task. These operating systems can operate in either batch mode or interactive mode. In batch mode, the operating system runs one program until it is finished. In interactive mode, you can modify the operation of the program using input from external sources, such as sensors, or a user interface device.

Multiple-process systems can be organized in three different ways:
- Multiuser: Systems that accommodate more than one user at a time.
- Multitasking: Systems that perform more than one task at a time
- Multiprocessor: Systems that divide the processing load into threads and distribute them among various    processors

In multiuser and multitask operations, simultaneous operations are displayed by switching among various tasks in a predetermined order. The multiuser system switches among users at multiple locations, whereas multitasking systems switch among various applications at a single location. In a large multiple-user system, the operating system is stored on the disk and you can load sections into RAM when required. This type of operating system must control several pieces of hardware, manage files created and used by users, provide security for information about each user, and manage communications among different computer systems. The operating system is also responsible for presenting each computer system with a user interface that can accept commands and data from the user. This interface can be a command line interpreter or a Graphical User Interface (GUI).
In a multiprocessor operating system, tasks are divided into subtasks, which are distributed among multiple microprocessors. This type of operation is referred to as parallel processing. The following figure shows all three types of multiple process operating systems.While simple microcomputers store the entire operating system in Read-Only Memory (ROM), most microcomputers use a bootstrapping process to load the operating system into Random Access Memory (RAM). In the bootstrapping process, a program called the bootstrap loader loads the operating system into memory from a ROM chip, floppy disk, hard disk drive, or another computer.
The term bootstrap refers to loading of the operating system along with its system files into RAM. In personal computers, the ROM Basic Input/Output System (ROM BIOS) performs the bootstrap operation. ROM BIOS is considered as an integral part of any chipset model because it supports the register structure of a particular chipset.

Multiple Process Operating System

To end this introduction i will remind what is ROM and RAM:

Read-Only Memory (ROM): This memory acts as the short-term storage for the personal computer while it processes data.
Random Access Memory (RAM): This memory is quick enough to operate
directly with the microprocessor and can be read from and written to as often
as required.
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