Advanced Micro Devices Inc (AMD)

[HailMary]

I presume you mean Compatibility Mode within Long Mode (there is no '64-bit compatibility mode').

Yes that is what I meant.

In AMD64, Long Mode totally gets rid of segments.

A quote from page 77 of the system programming manual (beginning of chapter 4):

In long mode, the effects of segmentation depend on whether the processor is running in compatibility mode or 64-bit mode:
- In compatibility mode, segmentation functions just as it does in legacy mode, using legacy 16-bit or 32-bit protected mode semantics.
- 64-bit mode, segmentation is disabled, creating a flat 64-bit virtual-address space. As will be seen, certain functions of some segment registers, particularly the system-segment registers, continue to be used in 64-bit mode.

My original message was based on table 2-6 from the section you had pointed out. I just went back and found the above, which is more clear.

x86 legacy lives on. long live x86!

Oh well. I'm not sure it matters much for now. Long term some of this baggage needs to be shed, as it is a disadvantage.