DS Games Don't Use SD Cards — They Use Proprietary Cartridges

Nintendo DS / DS Lite / DSi / 3DS games are on "Game Cards" (mask ROM or flash), not SD cards.

Physical Differences

DS Game Card	SD Card
Proprietary shape (notched corner)	Standard rectangular
Read-only (retail) or save flash (small)	Rewritable storage
Bus: SPI-like, encrypted	SDIO / SPI
Capacity: 8MB – 512MB (later 1–2GB)	Up to 2TB (SDXC)

DSi / 3DS: SD card slot for photos, sound, DSiWare/3DSWare downloads, save backups (some games). Not for retail games.
Flashcarts (R4, Ace3DS, R4i Gold 3DS+): MicroSD → DS Game Card adapter. Runs homebrew/backups. Legal gray area.

Retro game = cartridge. Save/extra data = internal flash or SD (DSi/3DS only).

Nintendo DS