I have problems wrapping my head around MBR, GPT, UEFI, and BIOS.
I understand that BIOS and MBR were first. BIOS is located on the mainboard and is what makes a PC with all its hardware startup.
The MBR is the first part on the hard drive which contains information about how the partitions of the hard drive are arranged and where the BIOS has to look to start up the OS located on the hard drive.
And this how I remember it working when there are multiple hard drives with an OS on it. The BIOS itself would pop up a menu asking which OS from which hard drive I want to start.
Now UEFI and GPT are where I lose it. Both are newer/updated versions of BIOS and MBR. As far as I understand UEFI has some general improvements and is designed to work with a hard drive that uses GPT which allows for more partitions and bigger drives. So why is UEFI so much different to BIOS and what the hell is GRUB in all of that.
I thought the thing that makes the OS on a hard drive start (bootloader) is baked into BIOS and UEFI, so why do I have to install like a custom one?
And it gets even weirder when combining Windows and Linux.
Let's say I have two hard drives plugged into my UEFI motherboard.
Disk A: Windows, GPT
Disk B: empty
Now I install Manjaro on the Disk B, I pick the MBR option, but then it looks like this:
Disk A: Windows, GRUB, GPT
Disk B: Manjaro, MBR
And in the UEFI menu it looks like this:
Manjaro (Disk A)
Windows (Disk A)
So does this mean I now have two separate bootloaders on my Disk A? One by Windows and the other one being GRUB which actually leads to Manjaro or Windows?
Why all of this fuss? Why cant the bootloaders be on the hard drive where the OS is actually located and UEFI asks you which one you want to start?
Is it safe to remove the GRUB on Disk A without breaking Windows or the bootloader for Windows? (When I tried Kubuntu it seemingly replaced the windows bootloader with GRUB and when I wanted to uninstall Kubuntu it failed to properly restore the Windows bootloader which made it unable for me to start Windows again)