[p_l]

a Type 3 UEFI implementation has no CSM, Type 2 has CSM available, Type 1 enforces booting into CSM (what many "BIOS"es actually was in later days)

[EvanAnderson]

Thanks for that. That sent me down an enjoyable rabbit hole. I got started with PCs back in the 80s and became fairly familiar with how boot worked back then. UEFI happened while I was paying attention to other things and I've never become as familiar with it as I should be. This was a good excuse to do some reading.

[deaddodo]

Just for clarification's sake, the proper terminology is "UEFI class" not "type".

Otherwise, this is accurate.