One excellent way to get started modifying your favourite game is to use memory hacking techniques. By learning what memory locations are used for specific functions you can perform all sorts of crazy cheats and start to get an understanding of how the game works internally.
You can even use a tool like Cheat Engine to inspect memory of an emulator such as Mupen64 to modify the contents of N64 game memory!
So we know that anything that can change in a game will be stored in some sort of Writable memory such as RAM.
This means that there are a number of bytes in RAM which corrospond to an interesting value in-game such as the Lives of the Player, or well anything at all really.
If we can find where these locations are we can change how the game behaves in real-time. But how do we find out where the values are located in the big blob of bytes known as RAM?
Just like finding anything we perform a search, if we know the current game lives are set to 3, then just loop over each byte in RAM until the value 3 and that should be the value right?!
Well sort of, it could be but the number 3 will also be used for many other non-lives related things in the game, for example an enemy could be located at position 3 on the Y axis etc. So we need to find out which location that has the number 3 corrosponds to the actual lives.
The technique is simple:
Now you can lock these memory addresses if you don’t want the game to change the stat, e.g you won’t lose HP.
Try to document these addresses and share your findings with the community, any new cheat codes or information about what memory addresses are responsible for what are always appreciated.
Any information you share can then give other Reversers a head start when they look into the same game and hopefully they will build on what you found, creating even more value for the community.
It is even possible to edit the memory of your favourite game on the original hardware, with no modifications required! Just use an old School Cheat Cartridge such as the Action Replay, Game Breaker or Equalizer cartridges.
These cartridges use a special syntax to tell the Nintendo 64 which memory addresses you want to modify and using that you can convert any cheat you have made in an emulator to run on physical hardware.
For example if you look for a life cheat code for Action Replay it will have the same addresses. You can then put this knowledge to the test and create your own cheat codes which run on physical Action Replay cartridges.
Memory Hacking is not exclusive to Emulators or cheat cartridges, the PC gaming community has been using these methods for many years. One very popular tool is known as Cheat Engine and it performs the same functions but for any PC program.