Question Curious about the order in which motherboards generally load connected hardware ?

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24hClocker

24hClocker

May 5, 2023
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Without really having any idea, I am guessing the following order (any expert is welcome to present the correct order):

1. CPU
2. RAM
3. Graphics (including screen)
4. HDD
5. USB, Audio and similar
 
As I recollect...the very first thing is a part of the CPU will fetch some BIOS code and begin executing instructions to finish initializing itself and RAM and to find and access system drives. Then it should be able to find and fetch UEFI from the UEFI partition which has the VGA driver to output graphics mode to the GPU and monitor, that's when you get the pretty logos during the rest of POST. Once it finishes POST it transfer control to the OS (bootloader for Windows, I think it's called Grub or maybe Grub2 for most Linux distros) to finish starting up the OS, which has it's own order based on various things and can be specific to each installation.

If UEFI isn't installed it uses compatibility mode which outputs text mode to the monitor instead until it transfers control to OS which had best be located in a specific sector of the drive indicated in CMOS settings. It will execute any code it finds there and do whatever it says...even if to simply tell you to call a number for access to your data.
 
Last edited:
lvt said:
The order may vary from motherboard to motherboard depending on how the Bios works on that model.
Click to expand...
Is it possible for the Bios to load faster than the motherboard so that a part of the hardware is undetected at Cold Boot?
 
In a modern system with secure boot, or some other security system in place (like Apple's T2), the process is generally:
  • Security chip verifies the motherboard firmware
  • If the security chip is happy with the firmware, it passes it on to the main CPU
  • Two things happen around the same time at this point
    • Main CPU initializes itself (sets up caches, cores, clock speed,etc)
    • PCIe devices power up and go through their own boot up process
  • Memory Management Unit is set up
    • The PCIe controller in the CPU is also likely setup at this point too
  • RAM is initialized
  • CPU looks at what PCIe devices are up and running and see what else they need
    • For example, PCIe devices can't actually draw more than 25W (from the slot anyway) until they negotiate with the PCIe controller that they're a high power device
    • In addition, PCIe devices may have a so-called option ROM that needs to be loaded. A device that has an option ROM you're likely familiar with are video cards, whose option ROMs allow the PC to display something before loading an OS
  • If everything checks out, the system looks at all the storage drives connected to it and sees which one has a bootloader. The first storage drive that it checks that has one completes the boot process.
    • The order of which the system checks is a firmware option
 
drea.drechsler said:
As I recollect...the very first thing is a part of the CPU will wake up, fetch BIOS code and begin executing instructions to finish initializing itself and RAM and to find and access system drives. Then it should be able to find and fetch UEFI from the UEFI partition which has the VGA driver to output graphics mode to the GPU and monitor, that's when you get the pretty logos during the rest of POST. Once it finishes POST it transfer control to the OS (bootloader for Windows, I think it's called Grub or maybe Grub2 for most Linux distros) to finish starting up the OS, which has it's own order based on various things and can be specific to each installation.

If UEFI isn't installed it uses compatibility mode which outputs text mode to the monitor instead until it transfers control to OS which had best be located in a specific sector of the drive indicated in CMOS settings. It will execute any code it finds there and do whatever it says...even if to simply tell you to call a number if you want to get access to your data.
Click to expand...
The reason that I am wondering about load order is that my laptop always goes automatically into Bios at every Cold Boot. It fires up fast and goes into Bios fast aswell but it says it cannot detect any harddrives or anything connected to USB. This made me think that Bios might be "rush-booting" at cold boot and not giving the harddrive enough time to wake up. And then i figured that USB-detection would be next in line after hdd-detection and therefore they also do not get detected. A simple restart always boots the laptop as normal.
 
24hClocker said:
The reason that I am wondering about load order is that my laptop always goes automatically into Bios at every Cold Boot. It fires up fast and goes into Bios fast aswell but it says it cannot detect any harddrives or anything connected to USB. This made me think that Bios might be "rush-booting" at cold boot and not giving the harddrive enough time to wake up. And then i figured that USB-detection would be next in line after hdd-detection and therefore they also do not get detected. A simple restart always boots the laptop as normal.
Click to expand...
Is the hard drive a spinner? (not an SSD). It may be spinning up slowly.

Also, do you have a UEFI installation? Or is it a legacy BIOS? If it's UEFI, try changing to compatibility mode (called CMS) and tell it the specific drive the OS partition is installed on and see if that changes anything.
 
hotaru.hino said:
In a modern system with secure boot, or some other security system in place (like Apple's T2), the process is generally:
  • Security chip verifies the motherboard firmware
  • If the security chip is happy with the firmware, it passes it on to the main CPU
  • Two things happen around the same time at this point
    • Main CPU initializes itself (sets up caches, cores, clock speed,etc)
    • PCIe devices power up and go through their own boot up process
  • Memory Management Unit is set up
    • The PCIe controller in the CPU is also likely setup at this point too
  • RAM is initialized
  • CPU looks at what PCIe devices are up and running and see what else they need
    • For example, PCIe devices can't actually draw more than 25W (from the slot anyway) until they negotiate with the PCIe controller that they're a high power device
    • In addition, PCIe devices may have a so-called option ROM that needs to be loaded. A device that has an option ROM you're likely familiar with are video cards, whose option ROMs allow the PC to display something before loading an OS
  • If everything checks out, the system looks at all the storage drives connected to it and sees which one has a bootloader. The first storage drive that it checks that has one completes the boot process.
    • The order of which the system checks is a firmware option
Click to expand...
So if my laptop doesn´t detect any bootable harddrive at Cold Boot that would then mean that some of the above verifications do not check out? Anything connected to usb is also not detected in Bios on Cold Boot. Save&Exit from Bios and a restart always fixes the boot into Windows. Any guesses what exactly might be going wrong with my laptop?

Edit: CPU, RAM and Graphics are detected at Cold Boot.
 
Last edited:
drea.drechsler said:
Is the hard drive a spinner? (not an SSD). It may be spinning up slowly.

Also, do you have a UEFI installation? Or is it a legacy BIOS? If it's UEFI, try changing to compatibility mode (called CMS) and tell it the specific drive the OS partition is installed on and see if that changes anything.
Click to expand...
INTEL SSDPEKNW512G8

UEFI Bios. Going to check if I can find that option. (Edit: Nope, didn´t find that option)
 
Last edited:
24hClocker said:
So if my laptop doesn´t detect any bootable harddrive at Cold Boot that would then mean that some of the above verifications do not check out? Anything connected to usb is also not detected in Bios on Cold Boot. Save&Exit from Bios and a restart always fixes the boot into Windows. Any guesses what exactly might be going wrong with my laptop?
Click to expand...
Not detecting a boot drive could be an issue with either the drive itself, the connection, or the controller its attached to. The first two are the more likely causes of the problem. If a component doesn't seem happy, depending on how necessary it is for the computer to run, the computer will either declare POST failure or it'll just pretend it doesn't exist.
 
hotaru.hino said:
Not detecting a boot drive could be an issue with either the drive itself, the connection, or the controller its attached to. The first two are the more likely causes of the problem. If a component doesn't seem happy, depending on how necessary it is for the computer to run, the computer will either declare POST failure or it'll just pretend it doesn't exist.
Click to expand...
I hope that you are not saying that the likely problem is that some part of the Motherboard is faulty and cannot handle cold boot? :) Why would it not find my keyboard and mouse connected to USB just because the HDD is not detected?
 
24hClocker said:
I hope that you are not saying that the likely problem is that some part of the Motherboard is faulty and cannot handle cold boot? :) Why would it not find my keyboard and mouse connected to USB just because the HDD is not detected?
Click to expand...
My guess is something happened to the board that caused multiple components to fail. Not detecting a hard drive is not related to USB functionality.

... I mean is this topic asking how things work, or is this trying to trouble shoot an actual problem?
 
hotaru.hino said:
My guess is something happened to the board that caused multiple components to fail. Not detecting a hard drive is not related to USB functionality.

... I mean is this topic asking how things work, or is this trying to trouble shoot an actual problem?
Click to expand...
Both :) I am truly curious to how I can be writing in Windows booted on the very same hard drive that cannot be detected on cold boot and on the keyboard that is not detected on cold boot.
 
hotaru.hino said:
If you have some sort of fast boot feature enabled on the computer (this is completely different from Windows' Fast Startup feature), then it'll only do the bare minimum to get a computer up and running. Since USB devices are usually not required for booting, it's very likely it's not bothering checking what's there.
Click to expand...
Fast boot is disabled in Bios. Same problem.

I am going to try updating Bios next to see if that changes anything. But I doubt that is the problem.
 
This sounds like you have a real hardware problem going on and not software related
 
SkyNetRising said:
Failing SSD probably.
Check health of the drive. Use Intel SSD tool.
Click to expand...
I have run Intel Solid-State Drive Toolbox. Read Scan & Data Integrity Scan, OK. No issues there. If it is a SSD problem I guess it might not show up when the SSD is warm. Problem only appears when cold.
 
At this point I do not think that I can do anything more? Everything check´s out fine when all the hardware is warm enough. There ought to be a tool that runs diagnostics before Bios loads, but that doesn´t exist. So I am left with this questionmark. Sad if I waste money on a new Solid-State SSD and that doesn´t fix the problem, since it tests fine. One thing that is clear is that there is a hardware malfunction. Taking it to a computer repair shop for troubleshooting is also not an economically viable solution.

Does someone have any final ideas?
 
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