@Gyroplast I know some of these words.gif

This somehow contradicts what both my BIOS is suggesting (it explicitly lists a boot order for physical drives, including both UEFI and legacy) and information I've been getting on the EndeavourOS forums.

(a) Windows claims to be using legacy mode (see previous post), so there should not be an ESP in the first place? I don't know what either legacy or UEFI does or means, and all the explanations I've found were highly political.

(b) FWIW, it seems that U/EFI (that's two different things I reckon?) requires its own partition, which it can have: If there's two drives, there can be two EFI partitions.

(c) This tracks with what I've been told on forums: As long as I'm happy with choosing the boot device on a BIOS-level, neither Linux needs to know about Windows, nor vice-versa. That's fine by me. From the perspective of the currently-booted OS, the other drive will show up as partitions, some of which are unvailable (I assume)

(d) Or, to turn (c) on its head: I only need to care about boot loaders if I want two OS's to share a physical drive.

(e) Now, the dual-booting guide for Arch specifically recommends using MTB/legacy mode when pairing with an already-installed legacy mode OS. I don't see a downside to this.

Last but not least: Turns out I borrowed my last M.2 screw when gifting an NVMe to a friend on Christmas. So the project's on hold until I can procure a new one. With how Deutsche Post is doing these days, that'll be a week at least (I wish I was exaggerating; we only get letters once a week in the middle of Hamburg). By then, I won't have time anymore, so the project's more or less dead in the water.

That's an anticlimatic ending if I've ever seen one.

@Gyroplast Wait. Shouldn't I just be able to bypass the entire bootloader headache by using either the Win or Arch drive as boot device? They don't really need to interfere with one another, I'm fine with pressing F12 to make a choice.

Only question is if the EndeavourOS installer messes with my Win drive's boot partition. Hmm.

@Gyroplast Thank you for your encouragement!

I'd leave the Windows SDD untouched as it is, I've got an extra 2 TB disk for Linux experiments. Far as I can tell, via German msinfo32, I'm running a Legacy ("Vorgängerversion") bootloader with secure boot disabled

So far, so good?

@NexCarter I'm not sure a full functional backup is even possible with Windows. Critical data is mirrored either way, but I need a functional fallback system if my Linux adventures lead me astray.

Hence the second hard drive for Linux specifically, to leave it in a self-contained box. But.. boot loaders are scary.