CycloDS is a company that provides blank cartridges for Nintendo DS and DS Lite SD. The cartridge is used to make e-books, games, mp3s, and movies playable. A SD card is also required. There are many benefits to using SD cards. A Nintendo DS only has so much storage before you run out of room. With SD cards, once you run out of room you can simply go out and buy a new one without losing any of your data. A normal MicroSD card can hold up to 2GB, while a MicroSDHC can hold up to 32GB.