This might seem like a rather basic question, but I'm having a lot of trouble tracking down an answer...
How does EFI actually find stuff to boot?
Under the old BIOS scheme, if the MBR has a special marker than the contents are loaded into RAM and executed. What happens next depends on what that code does. In short, to make an OS bootable, you need to install the boot-loader of your choice into the MBR, and then do whatever else your chosen boot-loader expects in order to configure it. Usually the BIOS has some menu to let you configure which order it searches for a bootable MBR, but that's it.
Under EFI... I have literally no idea how this stuff works. As best as I can tell, it doesn't involve boot blocks at all, and only involves the EFI System Partition. But I can't find any details beyond that. Do the files in this partition have to be in a certain folder or named a particular way? Because my test laptop is totally ignoring anything I put there.
Secure Boot adds a second layer of fun to this. In order to work, a binary has to be signed. But I can't figure out whether the signature is inside the file itself, or whether there's supposed to be a seperate signature file next to it...