Editing NX bit (section)

{{short description|Technology used in CPUs}}
The '''NX bit''' ('''no-execute bit''') is a [[Central processing unit|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''').<ref name="arm-pte">{{cite web |title=ARM Architecture Reference Manual |url=http://www.arm.com/miscPDFs/14128.pdf |archive-url=https://web.archive.org/web/20090206061248/http://arm.com/miscPDFs/14128.pdf |archive-date=2009-02-06 |publisher=[[ARM Limited]] |pages=B4{{hyp}}8, B4{{hyp}}27 |quote=APX and XN (execute never) bits have been added in VMSAv6 [Virtual Memory System Architecture]}}</ref> The term NX bit is often used broadly to describe similar executable space protection technologies in other processors.