3.8.2 PC Boot Process.txt

Current Segment IndicatorPC Boot Process 0:00-0:14 One of the main jobs of the UEFI or legacy BIOS is to help you start the system. Several different processes occur when you first turn the computer on. Let’s take a look at what they are. Power to CPU 0:15-0:38 First, power is supplied to the CPU. T...

Current Segment IndicatorPC Boot Process 0:00-0:14 One of the main jobs of the UEFI or legacy BIOS is to help you start the system. Several different processes occur when you first turn the computer on. Let’s take a look at what they are. Power to CPU 0:15-0:38 First, power is supplied to the CPU. The CPU is hard coded to look at a special memory address for code that it can execute. This memory address contains a pointer or a jump program that tells the processor where to find the UEFI or legacy BIOS program. After it does, the CPU loads the legacy BIOS or UEFI program. Run POST 0:39-2:15 After the UEFI or BIOS starts, the first process run is the POST process. POST stands for Power-On Self Test. POST does several different jobs. First, it verifies the integrity of the UEFI BIOS code to make sure it’s uncorrupted. After the POST is satisfied that the integrity of the code is good, it then looks for the BIOS and the video card. The BIOS and the video card are checked and loaded. This allows the display signal to be sent to your monitor so that you can see what’s happening during the power on process. Once that’s done, POST checks to see if there are other add-in cards with BIOS programs. Not all add-in cards have their own BIOS, but some do. The last process that occurs during POST is a device check. The POST program goes through the system and checks all of the basic devices that are needed for the system to run, such as memory, the keyboard, and so on. Perhaps you’ve powered on a PC and gotten a keyboard error because you were leaning up against the keyboard or holding down a key during system boot up. POST was sending that error. The POST was trying to check the keyboard and determined that something was wrong because it was receiving a signal for one particular key character over and over again. POST knew that the keyboard wasn’t supposed to do that. So it assumed that something was wrong with the keyboard and displayed the error on the screen. Also, you may have noticed the little memory counter up in the top left corner of the screen when you first turn on your PC. That’s the POST program running. It’s testing your computer’s memory to see how much memory is installed in the system. Identify System Devices 2:16-2:36 After the POST tests are complete, the UEFI or legacy BIOS identifies other system devices. It uses the information contained in your EEPROM as well as the information supplied by the devices themselves to identify and configure hardware devices. This is where your plug-and-play devices are allocated system resources. Identify the Boot Drive 2:37-3:20 At this point, the UEFI or legacy BIOS searches for a boot drive using the boot order specified in the CMOS setup program. You can go in to your CMOS setup program and specify which device you want to boot off of. For example, do you want to boot off of your DVD drive first? Or do you want to boot off of your hard drive first? Maybe you want to boot off of a flash drive. You can configure those things in your CMOS setup program. The BIOS will search for that boot drive using that boot order. Then on that boot device, the BIOS searches for the master boot loader and loads the boot loader program. At this point, the BIOS stops controlling the system. Control is passed to the boot loader program. Load the Operating System 3:21-3:41 The boot loader program is configured to locate and load an operating system off of your boot device, whether it’s a CD, DVD, or hard disk. When it finds the operating system, it loads the kernel for that operating system. As the operating system loads, additional steps are taken to load all of the additional programs and configure the devices that are needed by the operating system. Summary 3:42-3:58 So let’s review. In this lesson we discussed how the boot process works. First, power is supplied to the CPU. The CPU loads the BIOS. The POST process begins and the BIOS identifies other system devices and identifies the boot drive. And lastly, the operating system is loaded.