Understanding The Boot Process

The boot process happens every time you turn your computer on. It is difficult to see because it happens so fast. When you press the power button, you will notice that a few minutes later, Windows XP, or Windows Vista, or whatever Operating System you use is all loaded.

Lets find out what really happens when you press the power button and turn your computer on. The process is called the boot process and this article will help you understand the concept better. A list of what typically happens in a pc is as follows, but it will differ depending on your bios and manufacturer.

1. The first step when you press the power button, is to turn the Computer Power Supply on. A ‘Power Good’ signal is sent to the motherboard after which the CPU then (understanding that the power supply is stable) looks for the ROM bios.

2. The ROM bios gives the CPU the first instruction, which is to run the POST (Power-On-Self-Test).

3. The bios is then checked by the POST and then tests the CMOS RAM. If there are no problems with this then the POST continues to check the CPU and hardware devices such as the Video Card, the secondary storage devices such as the Hard Drive, Floppy Drives, Zip Drive or CD/DVD Drives.

4. If errors are found, then an error message is seen on screen or a number of beeps are heard (POST beep codes). The computer sometimes uses these beep codes instead of displaying an error message because the video card has not yet been initiated or the card must have an error.

5. After this, the bios finds the video card and runs the video card’s bios. Usually, this is the first thing that modern machines display on the screen. After that the computer looks at the other devices and runs their bios’ if they have one.
6. The system configuration is then displayed by the bios.

7. More tests are conducted during the display, including the test that shows your computer testing the memory. If problems are found from now on they will be displayed in a text message on the screen.

8. Next, the bios searches for something that it can boot from. Under the boot sequence, this can be set in the CMOS. This can be set to the A: Drive (Floppy) C: (Hard Drive, Primary Partition) D: (CD/DVD Drive) or others such as the USB drive or network card (depending on the bios).

9. The bios will search for the Master Boot Record (MBR), once the target boot device has been selected. While searching for a hard drive it looks at cylinder 0, head 0, sector 1.

10. On finding a valid volume boot sector, the bios has done its job and hands over control to the Operating System that completes the booting process. A few hardware tests will also be conducted.

11. If a valid boot record is not found, the computer will display an error, the “Non-System Disk or disk error” Press any key and replace when ready
12. If a valid boot record is found but the Master Boot Record cannot be read by it, then the computer will display a message, “Disk boot failure, insert system disk and press enter”