Which of the following features makes logical processor cores appear as physical cores to the operating system?

The XD-bit (Execute Disable) is a security feature that marks memory pages as non-executable to help prevent buffer-overflow attacks - it has no relation to logical processor presentation.

Hyperthreading (Intel SMT - Simultaneous Multi-Threading) duplicates the architectural state of a core, exposing two logical processors per physical core to the OS scheduler. This allows the OS to dispatch two threads simultaneously on one physical core, improving CPU utilization without adding actual physical cores.

MMU virtualization (such as Intel EPT or AMD RVI) provides hardware-assisted memory address translation for virtual machines - it does not create additional logical processors.

64-bit architecture defines the width of CPU registers and addressable memory space - it does not affect the number of logical or physical cores presented to the OS.