NX bit

The NX bit (no-execute bit) is a processor feature that separates areas of a virtual address space (the memory layout a program uses) into sections for storing data or program instructions. An operating system supporting the NX bit can mark certain areas of the virtual address space as non-executable, preventing the processor from running any code stored there. This technique, known as executable space protection or Write XOR Execute, protects computers from malicious software that attempts to insert harmful code into another program’s data storage area and execute it, such as in a buffer overflow attack.

The term "NX bit" was introduced by Advanced Micro Devices (AMD) as a marketing term. Intel markets this feature as the XD bit (execute disable), while the MIPS architecture refers to it as the XI bit (execute inhibit). In the ARM architecture, introduced in ARMv6, it is known as XN (execute never).^[1] The term NX bit is often used broadly to describe similar executable space protection technologies in other processors.