CertiGuide to A+ (Operating Systems)  9  Chapter 0000:  How to Get There       9  II  How Operating Systems Work

II  How Operating Systems Work 1 Defining the Operating System

Before we get into the details of specific Operating Systems, it is useful to understand what an Operating System is, and what it does.

In your A+ Core studies, you learned that the CPU is the heart of the computer, responsible for controlling the activities that occur on it.

When the CPU is shipped to you from the factory, it knows how to perform various simple activities like "add 1 to this memory address" or "move 1 byte from this memory address to this memory address".

By themselves, these instructions aren't very interesting. Most people probably wouldn't wander down to the local computer store and give someone $1000 for a couple really big boxes whose talents consisted of the ability to move 8 bits from one location in memory to another.

However, the instructions become interesting when they are combined by a computer programmer into step-by-step sequences consisting of hundreds of instructions, and the step-by-step sequence is given to the CPU (central processing unit), the computers brain.

With the right sequence of instructions, the CPU knows how to accomplish many complex activities, that computers are known for today - sending email, playing the latest computer games, surfing the net, and even formatting the resume you want to send out as soon as you become A+ certified.

These sequences of CPU instructions are called computer programs.

A program is an ordered set of instructions, generally in a binary machine language specific to the CPU type on which it will run, which tells the CPU which steps to take, to perform one or more useful actions.

II  How Operating Systems Work 1 Defining the Operating System