I've been catching up on Angry Video Game Nerd on YouTube. I am greatly enjoying it and admire the man for playing all the originals.

Apparently someone sent him a mod of Megaman 2 that had somehow been placed on a Megaman 2 cartridge.

My curiosity is really piqued. How do people replace or modify the software that is already on a NES cartridge? I would have figured that stuff was all read-only.

How did people develop software for NES? Did they have to code something up on a computer first and then the code would be "printed" to a cartridge? How did the development tools work?

Cartridge are very interesting. Basically, they are boards that plug in the console's own board. Most of the time, the board will only have a read-only memory that the console will access to read the game's data. Sometimes, it will also have read/write memory for save-states. But it could also have extra chips, to add extra power/functions to the console (this was the case of Starfox/Starwing on the SNES). Of course, this would raise the cost of the cartridge, so it wasn't very common.

I'm not completely sure how people did code back in the day. I guess they could have a board that you'd connect to a computer and plug into the console. The board would then act as a bridge between the computer and the console. Once they were happy with the code, they'd sent it to be burnt in read-only memory chips.

Modifying an existing cartridge shouldn't be possible, unless you add chips inside.

There used to be some really interesting conversation regarding the SNES at least on the Secret of Evermore boards on GameFAQs involving a programmer/developer. Obviously it can't be too difficult to get information in the actual cartridge though, because we have things like Timegate Flashback Games where they reproduce things like Secret of Mana 2 (Seiken Densetsu 3 with a translation patch applied) and Terranigma which never released in the US (part 3 of the Soul Blazer and Illusion of Gaia series).

I remember ages ago a neighbor that had a cartridge console with one special cartridge that was open on one side with sockets for IC chips. He'd just change chips to play different games.




-k