3.8.2 The Boot Process

Learn the process that a PC undergoes when it's booting.

Power:

• Power to the CPU
• CPU looks for special memory address that contains it's code
• CPU code looks for pointer that holds location of the BIOS/UEFI program
• CPU loads and runs BIOS/UEFI

Run POST Checks

• POST verifies the integrity of the BIOS code to make sure it's not corrupted
• POST looks for the BIOS and video card, and verifies that they're there
  • this step handles boot display
• check for other addon cards and run their BIOS programs (if they have one)
• check all connected devices and verify that they're there and working properly

Identify System Devices

• BIOS identifies other system devices using info contained in the EEPROM chip and info provided by the devices themselves to configure hardware devices. This is how plug-and-play devices are automatically setup and allocated system resources.

Find the Boot Drive

• BIOS looks for and runs the boot drive per instructions in the CMOS setup program
• When found, BIOS will look for and load the master boot loader program.
• At this point BIOS checks out and control of the system is handed over to the bootloader.

Load the OS

• Boot loader program looks for an installed operating system
• When found, the boot loader runs the OS's kernel, and then it runs all the programs that the kernel needs in order to function properly

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