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Chapter 1. DOS and the Personal Computer > What Happens When the Power Is Turne...

What Happens When the Power Is Turned On?

When you flip the power switch on your computer system, you set into motion a series of steps that must occur before you can see the DOS prompt, which signals that your computer is ready for use. No doubt you have seen these steps performed, possibly without realizing their significance. This set of steps is called booting the computer. This phrase refers to the old saying “pull yourself up by the bootstraps,” meaning to make something of yourself from nothing. That's exactly what booting does; it makes that expensive paperweight on your desk into a fully functional computer.

The first of these steps is the activation of the Power On Self Test (POST). The Power On Self Test is a program that has been recorded on a ROM chip located on the motherboard of your system. This program gets the ball rolling. First, it loads instructions into RAM for the CPU to follow. These instructions tell the computer to perform a quick self-diagnostic check of the hardware. One of the first things you see when you turn on the computer, therefore, is the system counting and testing the installed RAM.


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