• Terms
  • BIOS
  • Driver
  • POST
  • CMOS
  • MBR
  • Boot Medium
  • Boot Loader
• The Sequence

When a PC gets powered up it goes through a lot of processes before becomes ready for use. This is called the boot process. The boot process is controlled by the BIOS.

Terms

BIOS

The BIOS (Basic Input/Output System) is saved on the ROM component. The BIOS is integrated with the motherboard. In the BIOS you can configure the hardware components of the system. For example it’s possible to change the order at which the drivers are loaded or the clocking speed at which the processors should run at.

Driver

The drivers is a group of files which allow the operating system to communicate with connected hardware components. Without the drivers the operating system won’t be able to correctly control the devices attached to the PC.

POST

The POST (power-on self-test) is a small program that checks if there are any system errors. A beep from the PC indicated that everything is in order. Other beep sequences mean that something went wrong. All sequences translate to a specific error.

CMOS

The CMOS (complementary metal-oxide semiconductor) is a microchip designed to store information about the PC. It stores the system time, date and the chosen configurations of the BIOS.

MBR

The MBR (master boot record) is the first sector of the hard drive. A sector is most of the time 512 bytes large. It holds information on how the operating system should load and how the hard drive is divided.

Boot Medium

The Boot Medium also called the boot disk is the hard drive containing the MBR.

Boot Loader

The Boot Loader is a program designed to find and load the operating system. It is located inside the MBR

The Sequence

1. The power button activates the power supply. The motherboard followed by the other components are powered on.
2. The BIOS is loaded and executed.
   1. The POST program is executed.
   2. The information of the CMOS gets loaded.
   3. Other information such as the BIOS manufacturer, processor features, amount of installed RAM and amount of drivers are displayed on the monitor. These days tho a lot of PCs rather display the logo of the manufacturer.
   4. The boot medium with the MBR is searched.
   5. The MBR is loaded.
   6. The boot loader is loaded to RAM.
3. The BIOS gives execution control to the boot loader.
   1. The operating system is loaded.
4. The operating system takes control over execution.