Us slightly younger folk got to do similar stuff with cheat engines on consoles like the PSP. You'd configure a 'plugin' to be loaded by the CFW with the game, press some key combo to freeze the game and go fishing for cheats in memory (or use previously saved ones).

That kind of fiddling was such a big part of my developing an interest in computers and building a solid understanding of how all the magic works internally, it's a bit of a shame that kids nowadays can't really jump into fiddling around like that since the devices they'd play games on are much better locked down (or on PC, require you to already know what you're doing to be able to snoop around in another program's memory).

The memory cheats is how Game Genie worked!

On the playstation you would load the GG as a disc and then pop it open and load another disc, it felt like absolute hacker magic.

That’s what game genie was for cartridges too. You plug the game into the game genie into the console

All the Game Genies sat between the cartridge and console and intercepted and replaced accesses to specific ROM addresses. It didn't have the ability to access memory. Other devices like the Pro-Action Replay could modify memory and acted more like a TSR.

How would you figure out which memory location stored a given thing, e.g. # of lives?

I remember there were tools where you filtered all the matching values, then went back to game and played a little, came back filtered again, until one value stood out.

Indeed. I wrote an article a while back showing this in action with a Gamecube game running in an emulator: https://www.smokingonabike.com/2021/01/17/hacking-super-monk...

I remember doing this with the built-in tool of some emulator. They would let you filter by exact match and you could filter it down again after changing the value (losing a life).

But for stuff where exact matching wasn't practical like say a more or less continous health-bar, you could instead filter by searching for values that decreased / increased / didn't change.

Of course you would also have to guess at the data type but there weren't that many likely choices.

This is it. You'd mark the memory locations, go back to the game, repeat the search and filter down.

Either that, or you'd just go about trying one by one until you found it, then tried to figure out a pattern of what was around it and make notes on a paper for next time.

AFAIK Cheat Engine[1] is the standard approach. There are some cool tutorial videos on YouTube.

[1] https://www.cheatengine.org/

Hex editor with Ultima III I think we’d search for our character name and then start twiddling values until mom called us for dinner.

I forgot about that one! That was super nerdy and neat. Thanks!

That technique worked in Windows 95, too. I used to "cheat" on Diablo 1 using WinHex to max out my gold and modify some item stats.