Editing PEEK and POKE (section)

==POKEs as cheats==
In the context of games for many 8-bit computers, users could load games into memory and, before launching them, modify specific memory addresses in order to [[Cheating in video games#Memory editing|cheat]], getting an unlimited number of lives, immunity, invisibility, etc.  Such modifications were performed using POKE statements. The [[Commodore 64]], [[ZX Spectrum]] and [[Amstrad CPC]] also allowed players with one of the relevant cartridges (such as [[Action Replay]] or [[Multiface]]) to freeze the running program, enter POKEs, and resume.

For example, in ''[[Knight Lore]]'' for the [[ZX Spectrum]], immunity can be achieved with the following command:<ref>{{cite book | title = 20 Goto 10: 10101001 facts about retro computers | author = Steven Goodwin | year=2023 | isbn=978-1800182745}}</ref>
<syntaxhighlight lang="qbasic">POKE 47196,201</syntaxhighlight>
In this case, the value 201 corresponds to a [[Return statement|RET instruction]],<ref>{{cite book | title = Sinclair ZX Spectrum BASIC Programming | page=197 | year = 1982 | author1=Steven Vickers | author2=Robin Bradbeer | url = https://archive.org/details/spectrum-48-k-manual-original-manual-de-programacion/page/186/mode/2up}}</ref> so that the game returns from a subroutine early before triggering [[Collision_detection#Video_games|collision detection]].

Magazines such as ''[[Your Sinclair]]'' published lists of such POKEs for games. Such codes were generally identified by reverse-engineering  the machine code to locate the memory address containing the desired value that related to, for example, the number of lives, detection of collisions, etc.<ref>See for example, {{cite magazine | magazine = Your Sinclair | issue = 66 | date = June 1991 | title = Pokerama | url = https://archive.org/details/Your_Sinclair_066/page/n7/mode/2up}}</ref>

Using a 'POKE' cheat is more difficult in modern games, as many include anti-cheat or copy-protection measures that inhibit modification of the game's memory space. Modern operating systems enforce [[virtual memory]] protection schemes to deny external program access to non-shared memory (for example, separate [[page table]]s for each application, hence inaccessible memory spaces).