What is this thing sitting in slot 2 of my new DS lite?

Backup Game Boy Advance Cart Saves With a DS Lite nintendo ds lite gameboy slot Nintendo DS, DSi & DSiWare Topic: What is the slot called on the The slot on the bottom is for Gameboy Advance games iammikegaines nintendo ds lite gameboy slot Handheld gaming systems are having a moment While gaming on the go has been a thing since the Game Boy, the success of the Nintendo Switch

nintendo switch game card slot Spacer for DS Lite GBA Slot Cover replaces a missing PCB and allows the cover to stay in place