by AMD, as the NX bit, for use by its AMD64 line of processors, such as the Athlon 64 and Opteron.

After AMD's decision to include this functionality in its AMD64 instruction set, Intel implemented the similar XD bit feature in x86 processors beginning with the Pentium 4 processors based on later iterations of the Prescott core. The NX bit specifically refers to bit number 63 (i.e. the most significant