I'd been trying to find a permanent and proper way of adding large storage chips to the cartridge, and I finally found something viable: SD Cards on a Chip. They come in 1,2,4, and 8GB capacities, and have the SD controller built in. This could be hooked directly to the Pi GPIO pins, and would just show up as mass storage. I may be able to add a protected read only partition for ROM storage, and have the rest of the cart be available for user storage space. The Thonny Python IDE comes to mind here, allowing the user to store their programs on the cart, instead of having a separate storage device. I was going to simply add an SD card to every cart, but that gets expensive, fast. These chips are about $2.50 USD each, instead of the $9.00 USD or so for an SD card, plus the socket. I was worried about using SD cards as they might come loose over time and they'd certainly make the carts very expensive. Shaving $5.50 or so off each cart's manufacturing cost will help make the system affordable for, which gets it into the hands of more people. With just a blank memory cart, it would be nothing more than a giant flash card for the GPIO Port. The magic comes when other hardware is included in the cart, such as lights, speakers, mics, motor drivers, and whatever else you could want. It's basically just a hat system for the Pi 400, but with a few special features, like possibly being able to boot an OS from the GPIO Port. I was struggling to find flash storage large enough to hold even a few hundred megabytes until I came across this chip. The largest SPI flash chips I found were 8Mbits, so if have to connect a bunch of those up and program something to manage it. The SD system handles everything for me, getting this project going that much faster. I still plan on making some SPI ROM carts for simpler things and retro games. I like the challenge of making ROM carts and stuffing data into them like they used to do. I'm very excited to get some of these chips in for testing and start making my first cart.