Editing Undocumented feature (section)

== Hardware ==
Undocumented instructions, known as [[illegal opcodes]], on the [[MOS Technology 6502]] and its variants are sometimes used by programmers. These were removed in the [[WDC 65C02]].

[[File:CamelPark part9 bobbyborder11.png|thumb|A [[Commodore 64 demo]] using undocumented features to bypass the machine's usual screen border]]
[[Video game]] and [[demoscene]] programmers have taken advantage of the unintended operation of computers' hardware to produce new effects or optimizations.{{Citation needed|date=January 2023}}

In 2019, researchers discovered that a manufacturer debugging mode, known as VISA, had an undocumented feature on [[Intel Corporation|Intel]] [[Platform Controller Hub]]s (PCHs), chipsets included on most Intel-based motherboards, which makes the mode accessible with a normal motherboard.<ref name="Armasu_2019"/> Since the chipset has [[direct memory access]] this is problematic for security reasons.