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I don’t remember if Windows updates would cause it but installing Windows second definitely would. Likewise, I think upgrading (from say Windows 7 to 10) might. Basically Windows is just like “this MBR? It’s actually mine, thanks.” With no option to not erase it.
EFI systems don’t use the MBR. Windows will default to using the whole disk if you don’t use the “advanced” button, but so will most linux distro installers.
I’m talking about BIOS, yeah, sorry if it was unclear. My 2009 CPU is still hanging on. Barely.
2009 usually means you could indeed run it without an MBR: GPT format plus a very small (2MB) partition flagged to take over the functionality of containing a bootloader normally embedded in the MBR.
Correct. But Windows is not changing the BIOS boot order. It will however change your EFI to make itself the default boot again, even if you configured it to use a separate ESP on a completely separate disk and the boot menu residing there. That’s by design as you can access your efi settings from a running system via software, while your chances to change your BIOS settings from outside the BIOS are slim to non-existent.
Also every BIOS not decades old can indead run with a hybrid setup of GPT formated disk with a small partiton to replace the MBR functionality.