eli5: How did old NES cartridge games save your game?



I mean the ones like The Legend of Zelda that saved your game without the use of passwords. How was your game saved on the cartridge? Did it work the same way as an old floppy disk?

In: Technology

It saved on a small memory chip inside the cartridge. They had a small battery (much like, probably even identical to, the ones you find on computer motherboards).

After a long enough period of time those batteries do die and you do lose saved progress and the ability to save until you replace the battery (particularly anything you save is lost as soon as you remove power).

Games that had non-password save options had a battery inside which allowed the cartridge to store the save data when the console is powered off. See a picture here: https://www.dkoldies.com/product_images/uploaded_images/nesgamewithbattery.jpg

This holds true for other cartridge-based systems like the SNES/N64, Sega Genesis, etc.

They would typically have battery backed ram.

Flash memory wasn’t a thing yet, but RAM was. Specifically SRAM which stores data as different transistors being activated/deactivated. It looses data without power so there would be a coin cell on the board to keep your saves.

Cartridges in general were basically add-on computer parts, so they would come with RAM and disk memory and sometimes added processing power. The differences between graphics for example on the SNES level between launch games and games at the end wasn’t just upgrades in development, the hardware in the cartridge was significantly upgraded as well.

The cartridge has a RAM chip dedicated just for saving your game progress, and a little watch battery just to keep that RAM powered when the NES is turned off / the game is removed from the console.

I forget which exact chip is the game-save RAM, but you can see the battery in this picture of a crystal-clear NES cartridge. It’s the silver circle on the top left of the circuit board:


Fun fact: On the original NES consoles, you were warned to always hold the Reset button when turning off the console with a game that had save data. The original NES’s Ricoh CPU didn’t have any internal circuitry to make sure it powered off relatively gracefully, so random data could get written to random addresses when it powered off… including the game save RAM. Holding the Reset button would hold the CPU in a Reset state preventing this from happening.

>Did it work the same way as an old floppy disk?

Actually, yes, just probably not the version you played.

The first Zelda was released initially for the Japanese exclusive [Famicom Disk System](https://en.wikipedia.org/wiki/Famicom_Disk_System), a floppy-based addon to the Famicom that allowed bigger games, cheaper production, and yes, saveable games.

Previously gamers had to rely on passwords or a even a [clunky cassette tape addon](https://upload.wikimedia.org/wikipedia/commons/7/79/NintendoDataRecorderContents.png) to save their games.

You could even take a special disk to [kiosks](https://www.youtube.com/watch?v=EJCUT69IjSY) at some stores and download new games and extra content to it. 80s DLC!

Gaming Historian has a [great overview of it](https://www.youtube.com/watch?v=r9PuSrn_H1c).

It never released abroad and cartridge tech improving with battery saves and greater capacity meant games like Zelda could be released to the foreign market on cartridge.

There was a battery that powered a chip that kept the save game in memory.

If the battery fails (which is a likely result for those cartridges now) then the cartridge loses the functionality of saving the game, but everything else still works normally.