You would need to enable NX or XD in order to make your machine compatible with Windows 8

Windows 8 has a dependency on the NX bit of the CPU and we are unable to install the Windows 8 RP unless it is enabled.

NX stands for No eXecute and is a technology used in processors to prevent execution of certain types of code. This was originally invented by AMD.

XD is the acronym for eXecute Disable, which is an Intel specific implementation of NX. It refers to the same feature but Intel chose to call it by a different name.

XN is the ARM equivalent of the same feature and is the acronym for eXecute Never.

NX, XD and XN are essentially the same and we find they have different term for the same feature in AMD, Intel and ARM.