ROM Hacking, is basically using various tools to edit/modify/change the nature of a video game ROM image pulled from a game cartridge. Today, it probably looks like child's play, especially when you can just whip up a NES game from scratch with some online tutorials and a lot of trial and error, but back then, these things were so mysterious to us Millennials and older, that we simply felt it'd be easier just to take a pre-existing game, and modify it.

And these games came mostly via DOS based tools: Hexpose, Tile Layer, Mario Improvement...or even the bloody NESticle Emulator itself! Yes, NESticle would let you do pallet changes mid-game, and save them. It also would let you do modifications to the pattern tables and apply those changes as well - wild stuff.

A lot of editing though, was done with a Hex Editor - which was a tool like Hexpose that would let you see the code inside the game ROM in Hexidecimal (a power of 16 numbering system that starts at 0 and ends in "F" - ie 01234567890ABCDEF - and would represent it's data like below....