For those who didn't live through the era, it's hard to understate how much a Game Genie really did make things more fun and interesting. The thing basically gave you a huge menu of settings/tweaks you could make to a game, more common examples being "99 lives" or "Maximum HP" or something like that, but it could also make games more difficult for those who wanted that. It really felt to me like bumpers at a bowling alley, except the bumpers could be moved around to make it easier to get a strike or nearly impossible.
I never got one myself, but a friend did and we had endless fun tweaking different properties of all of our games. It was much more about exploration than it was about "cheating" at games. Game Genie was one of my first experiences of being mindblown at somebody's clever hack and use of technology, and I am grateful to have been able to live through that age.
In some cases they could be used to get things that were in the game "legitimately" but which you might not have access to. E.g. getting Mew in Pokemon Blue/Red or Surfing Pikachu in Pokemon Yellow.
Sometimes the codes would break in interesting ways. For example, an invincibility code might cause problems if it was on during a battle that you are scripted to lose. Or the "invincibility" code might actually work by instantly healing you; so you might find out that you are vulnerable if an enemy is strong enough to take all of your health with a single hit.
Like the parent post said, there was a lot of experimentation even when everything was working "correctly".
Pokemon Red (Game Boy SP + Game Genie) unlocking the unobtainable Mew (which Nintendo only gave away at rare in-person tournament events) at game start:
Zelda Link's Awakening (Game Boy + Game Genie) changing the value of "1" rupee to "255" rupees for effectively infinite currency (the creator isn't aware of the significance of "255"):
Banjo-Kazooie (N64 + Gameshark) replacing the main characters with the Rareware logo and adding an "infinite jump by pressing A" hack, which adds displacement or velocity with a button press (yes, this is totally absurd):
Goldeneye on N64 had some really cool hidden modes that could only be turned on with Game Genie. I don't recall which ones exactly required the Game Genie, but I'm pretty sure there was one that made everyone invisible until their first death in multiplayer. That was a lot of fun.
You're right that N64 did not have Game Genie (Super Nintendo and Sega Genesis also did), but N64 did have Gameshark, which was the spiritual successor to Game Genie (along with Action Replay). There is a project (https://github.com/JCR64/GoldenEye-007-N64-Gun-Game) that adds games to Goldeneye via Gameshark
The game genie did not give you a menu, you inputed codes which would persistently modify the memory map of the cartridge allowing for things like 99 lives or max Hp. The “menu” you describe was a booklet containing every game and a list of code changes.
Of course you could write in your own codes and make your own hacks but a lot of the time you ended up with garbled graphics or an unbootable game. They did keep this developer documentation to a minimum and this was before the internet. Although my local BBS had an ascii document detailing game genie’s internals and how to write your own codes, it was far from the reach of most 10 year olds
The game genie knockoff clone (I forget the name but remember the ads lol) had all of the codes in memory and as such gave you a menu to choose from
I managed to figure out hacking NES Game Genie codes pretty well at about 14, even without any documentation besides the Genie book itself.
I'd read enough library books about computers to understand binary and hexadecimal. So from the existing codes in the Genie book (like 5 lives / 99 lives / etc), I figured out how those values were coming from some of the letters defining binary/hex values. So I could extrapolate to more codes for different values. And from there I realized the other letters must specify the memory location, so I could bump that too and change some different stats that weren't in the book. I particularly had fun with Final Fantasy 1, where I figured out how to set inventory values and even tried out-of-range values and got items that didn't exist.
What I didn't know until years later was the difference between 6-letter (3 byte) and 8-letter (4-byte) codes. The additional byte in the longer code specifies a value such that the override takes place only if the memory location already equals that value. The purpose is to handle bankswitching (memory mappers), to have the code active only when the correct memory bank is. In practice, what this meant was that randomly trying 8-letter codes almost never did anything (1/256 that you happen to hit the right value) and so I only tried the shorter ones, and found a few weird effects from them.
>Of course you could write in your own codes and make your own hacks but a lot of the time you ended up with garbled graphics or an unbootable game.
My favorite one I ever randomly got was on one of the Mega Man games. The bullets had no momentum but still worked. You could "place" a bullet and the enemy would walk into it and die.
> The game genie did not give you a menu, you inputed codes which would persistently modify the memory map of the cartridge allowing for things like 99 lives or max Hp. The “menu” you describe was a booklet containing every game and a list of code changes.
Yes definitely, I meant the booklet as the "menu" (just like many restaurants give you a menu that is like a booklet) and decided to call it that so it would be more relatable, but yes it was just a series of codes, but codes you read off the paper similar to a menu (or maybe better, a dictionary or index?)
I never used the knockoff clone, but now I'm feeling some very, very delayed FOMO :-D
(Edit: I think the story below was for the original Playstation, with it's action-replay expansion port module. Should still have it somewhere in storage )
I also remember it having a serial or parallel port (at least the european Action Replay did), which you could hook upto a PC and with some debugging-software, do things like runtime memory manipulation, breakpoints and other nice debugging tools.
I think you could even run your own (small) binaries by sending them to the cartridge/addon, but this was ~20+ years ago, so the details lack me.
My favorite use of the Game Genie (Well, _Super_ Game Genie) was finding codes that would break a game in a way that made it more challenging--but not impossible--to play. Generally, this meant graphical glitches. But sometimes it meant stuff like changing how the character moved or making power-ups/items do random things.
I was one of the unfortunate suckers who paid around $100 USD to get one shipped from Canada before the US ban lifted, but it sure made renting games from video stores a lot more satisfying.
Games used to be fun through their gameplay mechanics and physics, rather than through their progression mechanics (legendary gear, maxed levels). Giving yourself max-stats would ruin most modern games, because the game world stops being interesting without the progression ladder.
Also, making a Nintendo-brand version of these would have been easy money, dunno why Nintendo stockholders were okay with less money.
Back then these sort of things were seen as tampering with other companies' ip. It was sort of taboo for any reputable business to build products like that.
Game Genie was likely the primary contributor of exposing kids to computer science in the 90's/00's, especially with "63" or "FF" appearing in every Infinite Lives cheat code. The "wow" moment for me was a Encounter the Specified Pokemon cheatcode for Pokemon Red where the specified Pokemon was their ID in hexadecimal.
Once I got a GameShark which included a VHS on how to create codes with the GameShark (identifying which memory addresses change and how to fix them to a specific value), and admittingly that may have scared me off of the computer science path.
> especially with "63" or "FF" appearing in every Infinite Lives cheat code
Except that those numbers did not commonly appear in Game Genie codes, because Game Genie codes are [trivially] enciphered. See e.g. https://gamehacking.org/library/114 for an explanation — the cipher used was different for each system.
AFAICT this enciphering was done precisely to discourage third-party code creation. Galoob never made any explicit statements about why they did it, but I'd guess† it served as a kind of DRM for codes, so that Galoob could be the only source of them, and thus sell you code books or something.
If you're remembering "a cheat-code device that preceded the GameShark that had literal address:value codes, and became the default input format for cheat codes in NES/SNES/GB emulators", then you're probably thinking of the Game Genie's competitor, the (Pro) Action Replay.
---
† There was also possibility of a vague hope on Galoob's part of contracting with games studios to create and publish "licensed" codes — making their device into less of a "cheating device" and more of a kind of post-sales-marketing micro-DLC-publishing channel for games studios.
Think of the type of thing that you see in e.g. Nintendo Switch Online with "special editions" of games that are just the regular game with a code applied. Studios could have been putting out "special editions" after-the-fact by publishing [i.e. working with Galoob to publish] officially-sanctioned codes in gaming magazines.
This never materialized... probably because studios that wanted to do post-sales-marketing micro-DLC, had enough foresight to build it into the game, in the form of pre-written live logic whose only live codepath involves a long and esoteric title-screen button-combo no player would ever guess; or even pre-written dead logic, that can be made live by an executable payload encoded into a password-system password, or a link-cable / e-reader / wi-fi distribution.
It wasn't shorthand, I'm pretty sure it was basic obfuscation. It was done by shuffling bits around then translating to letters using an algorithm that I don't know off the top of my head, but is well-documented. To me it shows explicit intent to cause codes to be harder to make.
> Game Genie was likely the primary contributor of exposing kids to computer science in the 90's/00's
I"d say the internet and creating webpages with javascript probably had a slightly bigger impact on young programmers at the time, by maybe 3 orders of magnitude.
I said computer science specifically: for web development in the 00's, Neopets was by far the biggest contributor for exposing kids to the power of the internet, but that was more limited to HTML.
Codemasters being the company who made the Game Genie AND the best racing games out there is a square I've never been able to circle. It feels a tad unreal for me.
One of those studios that's always had massive talent, although I'm increasingly concerned about their future as EA tightens their grip on them.
game genie was amazing! still remember the commercial where the tv screen exploded.. i got a cd burner for Xmas in 1998, next step was a mod chip for my ps1. soldering it in was such a high risk, high reward project for a 14 year old. from buying the chip online with my parents credit card to buying the soldering iron and solder at radio shack with lawn mowing money, to disassembling the ps1 and following the directions ever so carefully. that first boot up was nerve racking. for the remainder of the ps1 era my friend and I would rent games, burn them, swap with each other and by the end we both had 200+ titles to choose from..a magical time indeed!
i remember figuring out that i had one of the lucky early-model dreamcasts that didn't require mod chips. coincided with the brief period where you could find pretty much anything on megaupload. i'm sure all of my burned games have disintegrated by now but i had an awesome collection of games back then :)
That article was bizarrely difficult to read. Light on any details, all over the place story narration and the author trying far too hard to tie it to fucking AI today.
Just talk about the game genie on its own merits, it's far more interesting than AI slop for some of us
I agree. It's an interesting side note that it was cited in the Anthropic case, but the way it was used in that case is so weird that it really took away from the whole thing. It just kinda made me angry (again) about LLMs using all the information for free and with no citations instead of happy and nostalgic for the game genie (which still didn't help me make it past level 2 in Ninja Gaiden, dang it!)
Yes, if the ruling allowing the GameGenie is about the freedom to tinker, I see this being an effective defence for building an AI myself from my own books for my own use. But, removing the need to buy the book in the first place is the key problem that the article seems to ignore.
Yeah I also thought that was a weird choice. The Game Genie is interesting on its own merits, there's no need for forced attempts to tie it in to the Current Thing.
Ah basically like the "Final Cartridge" or "Power Cartridge" for the Commodore 64? Stuff that'd freeze the machine and let you edit memory using hex codes?
I had the "Power Cartridge" on my C128. Fun times.
Not quite. The Game Genie presented a UI before the game started where you could enter codes. These codes were basically patches to the game's ROM. When the game ran, the Game Genie would intercept the requests for the bytes of ROM based off your code and replace them with a different value.
There was a prototype of a more advanced model that would be closer to what you're describing, but it never made it to market.
For those who didn't live through the era, it's hard to understate how much a Game Genie really did make things more fun and interesting. The thing basically gave you a huge menu of settings/tweaks you could make to a game, more common examples being "99 lives" or "Maximum HP" or something like that, but it could also make games more difficult for those who wanted that. It really felt to me like bumpers at a bowling alley, except the bumpers could be moved around to make it easier to get a strike or nearly impossible.
I never got one myself, but a friend did and we had endless fun tweaking different properties of all of our games. It was much more about exploration than it was about "cheating" at games. Game Genie was one of my first experiences of being mindblown at somebody's clever hack and use of technology, and I am grateful to have been able to live through that age.
Two other fun details:
In some cases they could be used to get things that were in the game "legitimately" but which you might not have access to. E.g. getting Mew in Pokemon Blue/Red or Surfing Pikachu in Pokemon Yellow.
Sometimes the codes would break in interesting ways. For example, an invincibility code might cause problems if it was on during a battle that you are scripted to lose. Or the "invincibility" code might actually work by instantly healing you; so you might find out that you are vulnerable if an enemy is strong enough to take all of your health with a single hit.
Like the parent post said, there was a lot of experimentation even when everything was working "correctly".
In the name of "Show, Don't Tell," here are some fun examples:
Super Mario Bros 3 (NES + Game Genie) equipping Hammer Suit / Invincibility:
https://www.youtube.com/shorts/FUVOM3rxZ5U
Super Mario World (SNES + Game Genie) causing weird memory distortion glitches, enabling swimming anywhere, and other more useful things:
https://youtu.be/o7_eFcpwq24?si=_io5oSzpRxdvuEMp&t=164
Super Mario RPG (SNES + Game Genie) enabling the hidden developer debug menu:
https://youtu.be/bH-uh9BnIfU?si=0L7qviRp5T-Nokjs&t=402
Pokemon Red (Game Boy SP + Game Genie) unlocking the unobtainable Mew (which Nintendo only gave away at rare in-person tournament events) at game start:
https://www.youtube.com/shorts/yzqTRbixnak
Zelda Link's Awakening (Game Boy + Game Genie) changing the value of "1" rupee to "255" rupees for effectively infinite currency (the creator isn't aware of the significance of "255"):
https://www.youtube.com/shorts/dRFqU_Dz3M8
Super Mario 64 (N64 + Gameshark) adding Dorrie the Plesiosaur to Lethal Lava Land:
https://youtu.be/DVBMdwn8Kc0?si=cUZ5ioG1GEvY0l-H&t=84
Super Mario 64 (N64 + Gameshark) showing off the Gameshark menu and a bunch of Mario character animation swaps:
https://www.youtube.com/shorts/AptK2MbqLXQ
Banjo-Kazooie (N64 + Gameshark) replacing the main characters with the Rareware logo and adding an "infinite jump by pressing A" hack, which adds displacement or velocity with a button press (yes, this is totally absurd):
https://www.youtube.com/watch?v=XF6pwm00vtY
Zelda Ocarina of Time (N64 + Gameshark) spawning a hidden developer-only enemy, the Starfox Arwing, which shoots lasers at Link:
https://www.youtube.com/shorts/KOQUhm1cNu8
Smash Bros 64 (N64 Emulator) spawning Master Hand (final boss) as a playable character in a standard stage:
https://www.youtube.com/watch?v=A1i9TRLifaw
Zelda Majora's Mask (N64 + Gameshark) spawning special items, equipping the wrong items, using the wrong weapons, manually adjusting the clock, etc.:
https://youtu.be/ae2q9CjqXsc?si=IPB7XcPFWZyzpbh3
Smash Bros Melee (Gamecube emulator) spawning infinite items and damage for total chaos:
https://www.youtube.com/watch?v=IDZZiL4rqlk
Quick Game Genie hardware overview:
https://www.youtube.com/shorts/WzHokvjdvDc
Goldeneye on N64 had some really cool hidden modes that could only be turned on with Game Genie. I don't recall which ones exactly required the Game Genie, but I'm pretty sure there was one that made everyone invisible until their first death in multiplayer. That was a lot of fun.
Game genie was only on regular Nintendo. Those other modes on goldeneye were an Easter egg built into the game, iirc
You're right that N64 did not have Game Genie (Super Nintendo and Sega Genesis also did), but N64 did have Gameshark, which was the spiritual successor to Game Genie (along with Action Replay). There is a project (https://github.com/JCR64/GoldenEye-007-N64-Gun-Game) that adds games to Goldeneye via Gameshark
I just liked to make everyone wear sunglasses. Plus loading the tank into every level possible.
From your first link - I apparently still have 'xnkxglie' memorized...
> E.g. getting Mew in Pokemon Blue/Red
0115D8CF is one of those sequences that is permanently burned into my brain to the same level as FCKGW
Wow. Talk about burn in. RHQQ2 I think was the next part. It's been over a decade since I used that code...
Mew can also be obtained through glitches without any game alteration devices.
The game genie did not give you a menu, you inputed codes which would persistently modify the memory map of the cartridge allowing for things like 99 lives or max Hp. The “menu” you describe was a booklet containing every game and a list of code changes.
Of course you could write in your own codes and make your own hacks but a lot of the time you ended up with garbled graphics or an unbootable game. They did keep this developer documentation to a minimum and this was before the internet. Although my local BBS had an ascii document detailing game genie’s internals and how to write your own codes, it was far from the reach of most 10 year olds
The game genie knockoff clone (I forget the name but remember the ads lol) had all of the codes in memory and as such gave you a menu to choose from
I managed to figure out hacking NES Game Genie codes pretty well at about 14, even without any documentation besides the Genie book itself.
I'd read enough library books about computers to understand binary and hexadecimal. So from the existing codes in the Genie book (like 5 lives / 99 lives / etc), I figured out how those values were coming from some of the letters defining binary/hex values. So I could extrapolate to more codes for different values. And from there I realized the other letters must specify the memory location, so I could bump that too and change some different stats that weren't in the book. I particularly had fun with Final Fantasy 1, where I figured out how to set inventory values and even tried out-of-range values and got items that didn't exist.
What I didn't know until years later was the difference between 6-letter (3 byte) and 8-letter (4-byte) codes. The additional byte in the longer code specifies a value such that the override takes place only if the memory location already equals that value. The purpose is to handle bankswitching (memory mappers), to have the code active only when the correct memory bank is. In practice, what this meant was that randomly trying 8-letter codes almost never did anything (1/256 that you happen to hit the right value) and so I only tried the shorter ones, and found a few weird effects from them.
>Of course you could write in your own codes and make your own hacks but a lot of the time you ended up with garbled graphics or an unbootable game.
My favorite one I ever randomly got was on one of the Mega Man games. The bullets had no momentum but still worked. You could "place" a bullet and the enemy would walk into it and die.
SXEZSKOZ - Skywalker
> The game genie did not give you a menu, you inputed codes which would persistently modify the memory map of the cartridge allowing for things like 99 lives or max Hp. The “menu” you describe was a booklet containing every game and a list of code changes.
Yes definitely, I meant the booklet as the "menu" (just like many restaurants give you a menu that is like a booklet) and decided to call it that so it would be more relatable, but yes it was just a series of codes, but codes you read off the paper similar to a menu (or maybe better, a dictionary or index?)
I never used the knockoff clone, but now I'm feeling some very, very delayed FOMO :-D
That's still a menu. Menu is also a generic term for any selection set, and menus printed on signs and cards are still called...menus.
(Edit: I think the story below was for the original Playstation, with it's action-replay expansion port module. Should still have it somewhere in storage )
I also remember it having a serial or parallel port (at least the european Action Replay did), which you could hook upto a PC and with some debugging-software, do things like runtime memory manipulation, breakpoints and other nice debugging tools.
I think you could even run your own (small) binaries by sending them to the cartridge/addon, but this was ~20+ years ago, so the details lack me.
You could also find new codes in magazines like Nintendo power which was always fun.
Was GameShark the knockoff you're thinking of?
It was the name of the game in PSX type stuff for this.
And they didn't obfuscate the hex addresses like the game genie did IIRC.
I hacked my own codes on things like xenogears and vagrant story , good times. Almost as fun as save file hacking
a list of known games and tested "well-behaving" codes
the really fun part was exploring building your own codes and how/why they worked or didn't
>The game genie knockoff clone
GameShark!
My favorite use of the Game Genie (Well, _Super_ Game Genie) was finding codes that would break a game in a way that made it more challenging--but not impossible--to play. Generally, this meant graphical glitches. But sometimes it meant stuff like changing how the character moved or making power-ups/items do random things.
I was one of the unfortunate suckers who paid around $100 USD to get one shipped from Canada before the US ban lifted, but it sure made renting games from video stores a lot more satisfying.
Games used to be fun through their gameplay mechanics and physics, rather than through their progression mechanics (legendary gear, maxed levels). Giving yourself max-stats would ruin most modern games, because the game world stops being interesting without the progression ladder.
Also, making a Nintendo-brand version of these would have been easy money, dunno why Nintendo stockholders were okay with less money.
Back then these sort of things were seen as tampering with other companies' ip. It was sort of taboo for any reputable business to build products like that.
Would rase a lot of questions: if the game is better if you choose the stats why dose it not let you without another device?
Game Genie was likely the primary contributor of exposing kids to computer science in the 90's/00's, especially with "63" or "FF" appearing in every Infinite Lives cheat code. The "wow" moment for me was a Encounter the Specified Pokemon cheatcode for Pokemon Red where the specified Pokemon was their ID in hexadecimal.
Once I got a GameShark which included a VHS on how to create codes with the GameShark (identifying which memory addresses change and how to fix them to a specific value), and admittingly that may have scared me off of the computer science path.
> especially with "63" or "FF" appearing in every Infinite Lives cheat code
Except that those numbers did not commonly appear in Game Genie codes, because Game Genie codes are [trivially] enciphered. See e.g. https://gamehacking.org/library/114 for an explanation — the cipher used was different for each system.
AFAICT this enciphering was done precisely to discourage third-party code creation. Galoob never made any explicit statements about why they did it, but I'd guess† it served as a kind of DRM for codes, so that Galoob could be the only source of them, and thus sell you code books or something.
If you're remembering "a cheat-code device that preceded the GameShark that had literal address:value codes, and became the default input format for cheat codes in NES/SNES/GB emulators", then you're probably thinking of the Game Genie's competitor, the (Pro) Action Replay.
---
† There was also possibility of a vague hope on Galoob's part of contracting with games studios to create and publish "licensed" codes — making their device into less of a "cheating device" and more of a kind of post-sales-marketing micro-DLC-publishing channel for games studios.
Think of the type of thing that you see in e.g. Nintendo Switch Online with "special editions" of games that are just the regular game with a code applied. Studios could have been putting out "special editions" after-the-fact by publishing [i.e. working with Galoob to publish] officially-sanctioned codes in gaming magazines.
This never materialized... probably because studios that wanted to do post-sales-marketing micro-DLC, had enough foresight to build it into the game, in the form of pre-written live logic whose only live codepath involves a long and esoteric title-screen button-combo no player would ever guess; or even pre-written dead logic, that can be made live by an executable payload encoded into a password-system password, or a link-cable / e-reader / wi-fi distribution.
Using the letters was just shorthand, I think you're overthinking it.
It wasn't shorthand, I'm pretty sure it was basic obfuscation. It was done by shuffling bits around then translating to letters using an algorithm that I don't know off the top of my head, but is well-documented. To me it shows explicit intent to cause codes to be harder to make.
> Game Genie was likely the primary contributor of exposing kids to computer science in the 90's/00's
I"d say the internet and creating webpages with javascript probably had a slightly bigger impact on young programmers at the time, by maybe 3 orders of magnitude.
This was way before javascript.
The first Game Genie was released for the NES in 1990.
The very first version of Javascript wasn't until 1995.
I said computer science specifically: for web development in the 00's, Neopets was by far the biggest contributor for exposing kids to the power of the internet, but that was more limited to HTML.
Not MySpace?
Codemasters being the company who made the Game Genie AND the best racing games out there is a square I've never been able to circle. It feels a tad unreal for me.
One of those studios that's always had massive talent, although I'm increasingly concerned about their future as EA tightens their grip on them.
The NES adaptor gives me flashbacks to my childhood. PS1 and PS2 mods had the same vibe. What a great era.
game genie was amazing! still remember the commercial where the tv screen exploded.. i got a cd burner for Xmas in 1998, next step was a mod chip for my ps1. soldering it in was such a high risk, high reward project for a 14 year old. from buying the chip online with my parents credit card to buying the soldering iron and solder at radio shack with lawn mowing money, to disassembling the ps1 and following the directions ever so carefully. that first boot up was nerve racking. for the remainder of the ps1 era my friend and I would rent games, burn them, swap with each other and by the end we both had 200+ titles to choose from..a magical time indeed!
That was how I felt following the guides to hack DirecTV for the first time.
i remember figuring out that i had one of the lucky early-model dreamcasts that didn't require mod chips. coincided with the brief period where you could find pretty much anything on megaupload. i'm sure all of my burned games have disintegrated by now but i had an awesome collection of games back then :)
The Game Genie allowed you to explore past levels you were stuck on.
That article was bizarrely difficult to read. Light on any details, all over the place story narration and the author trying far too hard to tie it to fucking AI today.
Just talk about the game genie on its own merits, it's far more interesting than AI slop for some of us
I agree. It's an interesting side note that it was cited in the Anthropic case, but the way it was used in that case is so weird that it really took away from the whole thing. It just kinda made me angry (again) about LLMs using all the information for free and with no citations instead of happy and nostalgic for the game genie (which still didn't help me make it past level 2 in Ninja Gaiden, dang it!)
Huzzah, information is free.
Yes, if the ruling allowing the GameGenie is about the freedom to tinker, I see this being an effective defence for building an AI myself from my own books for my own use. But, removing the need to buy the book in the first place is the key problem that the article seems to ignore.
Yeah I also thought that was a weird choice. The Game Genie is interesting on its own merits, there's no need for forced attempts to tie it in to the Current Thing.
Ah basically like the "Final Cartridge" or "Power Cartridge" for the Commodore 64? Stuff that'd freeze the machine and let you edit memory using hex codes?
I had the "Power Cartridge" on my C128. Fun times.
Not quite. The Game Genie presented a UI before the game started where you could enter codes. These codes were basically patches to the game's ROM. When the game ran, the Game Genie would intercept the requests for the bytes of ROM based off your code and replace them with a different value.
There was a prototype of a more advanced model that would be closer to what you're describing, but it never made it to market.