When the manual says that the segment bases are ignored in long mode, it is only referring to 64-bit code. As far as I remember, the terminology goes like this:

When the manual says that the segment bases are ignored in long mode, it is only referring to 64-bit code. As far as I remember, the terminology goes like this: 64-bit OS, running 64-bit user code -> "long mode" 64-bit OS, 16/32-bit user code -> "compatibility mode" 16/32-bit OS -> "legacy mode" Also I've personally tested that it works, without any virtualization required (see sibling comment). Wine also does it in order to run 16-bit Windows programs, or at least it used to at one time - IIRC, there was some discussion on the Linux kernel mailing list about it.