So imagine I have 2 HDDs, how does UEFI firmware decide what drive to boot from? Let's say the two drives have GPT tables on them in the very beginning of their address space?

  • Too broad to explain. In short, NVRAM stores that path of the EFI FAT partition. – Biswapriyo Mar 21 at 20:13
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    Bit more specifically it uses the GUID AKA partUUID to know which ESP to find boot files. Entries can use different ESP. You can see details:sudo efibootmgr -v and lsblk -o name,mountpoint,label,size,fstype,uuid,partuuid | egrep -v "^loop" to see which entry uses which ESP. en.wikipedia.org/wiki/EFI_system_partition & details: wiki.archlinux.org/index.php/… – oldfred Mar 21 at 21:14
  • Thanks for references – Artem Hevorhian Mar 22 at 7:20

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