3.WHAT IS AN OPERATING SYSTEM2?

In any device that has an operating system, there’s usually a way to make changes to how the device works. This is far from a happy accident; one of the reasons operating systems are made out of portable code rather than permanent physical circuits is so that they can be changed or modified without having to scrap the whole device.

For a desktop computer user, this means you can add a new security update, system patch, new application or often even a new operating system entirely rather than junk your computer and start again with a new one when you need to make a change.

As long as you understand how an operating system works and know how to get at it, you can in many cases change some of the ways it behaves. And, it’s as true of your cell phone as it is of your computer.

So, essentially, when you turn on your computer, the first program is a set of instructions kept in the computer’s read only memory. These instructions examine the system hardware to make sure everything is functioning properly.This power-on self test check

the CPU, the memory, and the basic input/output systems (BIOS) for errors and stores the result in a special memory location. Once the test has successfully completed, the software loaded in ROM (sometimes called the BIOS or firmware) will begin to activate the computer’s disk drives.

In most modern computers, when the computer activates the hard disk drive, it finds the first piece of the operating system: the bootstrap loader. The bootstrap loader is a small program that has a single function: It loads the operating system into memory and allows it to begin operation.

In the most basic form, the bootstrap loader sets up the small driver programs that interface with and control the various hardware subsystems of the computer. It sets up the divisions of memory that hold the operating system, user information and applications.

It establishes the data structures that will hold the myriad signals, flags and semaphores that are used to communicate within and between the subsystems and applications of the computer. Then it turns control of the computer over to the operating system.

It might be helpful for you to know the history of operating systems.