Computer Firmware Boot Principles and Windows System Boot Process: Part One
Computer Firmware Boot Principles: Windows System Boot Process | Part 1
During the Windows system startup process, there is a critical file that plays a guiding role in booting Windows—the BCD file, which stands for Boot Configuration Data.
If this BCD file has even a minor configuration error, we won’t be able to boot Windows normally, and instead, we’ll be greeted with an error blue screen or black screen.
Therefore, knowing how to repair the BCD file is an important skill. Not only does it deepen our understanding of how Windows boots, but it can also help us solve computer problems when it matters most.
Some might say we can simply use boot repair tools to fix the boot and repair the BCD, so there’s no need to learn how to manually edit and repair it.
In reality, no boot repair tool is a silver bullet. I’m not saying it will fail to repair—I’m saying that BCD booting requires a reasonable combination of software and hardware configurations, taking multiple factors into account.
Let me give you an example.
On a UEFI firmware system, I want to repair the Windows boot (BCD) on an MBR partition table disk. If we use a common boot repair tool (like Dism++), it will most likely repair the boot for a BIOS firmware environment.
However, our firmware is UEFI, not BIOS.
This is because Dism++ only knows the general boot repair mode—it assumes MBR partition table disks pair with BIOS firmware, and doesn’t know that UEFI firmware can also work with MBR partition tables.
This is just one small example. To make our computer’s boot mode better suit our usage habits, we need to configure the BCD boot menu in detail, and detailed configuration requires learning.
At the end of this article, I will explain the general methods for repairing boot on various firmware types.
Understanding the principles is the foundation of all learning and the source of all correct operations.
Through today’s article, I will explain in detail and in an accessible way how the Windows system actually boots and how it is guided.
If you’re willing to learn, follow my train of thought and thoroughly understand Windows booting.
If you have questions, feel free to join my WeChat group to ask.
Main Content Begins
Let’s start from the moment we press the power button.
Motherboard Powers On
The moment you press the power button, a circuit board inside your computer called the motherboard starts receiving power.
Once the motherboard is powered on, the next step is to load the firmware.
What is Firmware?
The term “firmware” might initially sound like a physical entity—something solid.
※ However, in reality, firmware is a miniature system, a piece of software, a set of code stored in the motherboard’s NVRAM.
NVRAM stands for Non-Volatile Random Access Memory.
In simple terms, NVRAM is a small module on the motherboard that can store data. Even without power, the data in NVRAM is not lost, similar to a USB flash drive.
In contrast, RAM is Volatile Random Access Memory, which is what we commonly call memory.
The characteristic of RAM is that without power, it cannot retain any data.
So when we shut down and restart, the computer’s state from the previous session is not preserved.
Types of Firmware?
Currently, there are two types of firmware: BIOS and UEFI.
- BIOS
- Used by older computers. Generally, computers manufactured before 2015 use BIOS, or have both BIOS and UEFI firmware.
- UEFI
- Used by the vast majority of modern computers. It generally supports backward compatibility with BIOS.
I won’t go into detail here about the advantages and disadvantages of BIOS vs. UEFI firmware. You can search for that on your own.
I will only introduce their differences and pros/cons when necessary.
Different firmware types mean different boot modes, and naturally, different boot methods.
Firmware Self-Test
After the motherboard powers on, it loads the firmware. Once the firmware is loaded into memory, it begins to run. The motherboard hands over full control of the computer to the firmware.
Both firmware types first need to inspect the hardware environment they’re running on—this is called self-testing (POST).
This is a very quick process. If it fails, the computer will get stuck at the first step: a hardware fault in the computer.
These are typically critical hardware failures, such as issues with the CPU, fan, memory, or display. We won’t discuss these hardware faults here. Let’s continue booting the computer.
From this point onward, the boot methods of UEFI and BIOS diverge.
We’ll first introduce the UEFI boot method, followed by the BIOS boot method.
Reading Order for This Series:
- Computer Firmware Boot Principles: Windows System Boot Process Part 1
- Comprehensive Reveal of UEFI Firmware Booting Windows Full Process
- Core Configuration: BCD File Detailed Explanation and BOOTICE Editing Practice
- BIOS Firmware Booting Windows System
- General Methods for Repairing Windows System Boot