From ivc wiki
The Nintendo DS system has two 3" lcd screens capable of 256 x 192 resolution, one being a touch screen, dual ARM7 and ARM9 processors, voice-recognition, and IEEE 802.11 and a proprietary wireless network format.
Update: Most of the older adapters are now obsolete and there is no need to keep a PassKey in slot 1 (DS) or flash the DS with the FlashMe or PassMe firmware. There are now slot 1 (DS) flash cards that can send program counters to slot 2 and act as a GBA cart, running from a DS slot 1 cart. These cards are also known as 2. generation flash cards.
There are three different ways to make the DS run homebrew code:
Use an external passthrough adapter that fits between a regular DS game and the DS slot on the machine that allows you to run code from GBA slot in DS mode. The game that is onto the adapter is needed for initial authentication. All it does is patching the first call, or load game command, that is directed to the DS slot and directs them to GBA slot. There are many different PassMe adapters out there, but the most popular ones are PassMe, PassMe2, SuperPass, G6 PassKey and MagicKey (MK).
Flash the on-board BIOS memory inside the DS. This essentially does exactly the same thing as the PassMe adapter above but you need to short a jumper (SL1) on the DS circuit board to be able to write to the BIOS memory. Even with this method you still need to have a DS game inserted in the DS slot. This method is called FlashMe and requires one of the other methods to flash the memory once, all upgrades after that can be directly without PassMe or Wifime.
Use the wireless capabilities of the DS. You can use a PC with a specific wireless network adapter, special drivers and software, to send applications wirelessly to the DS. This method utilizes a exploit in the 'DS Download Play' menu option that you can see when you power on the system without a game inserted. This method is call WifiMe / Wireless Multiboot.
All of these methods can load applications and games from the GBA slot, and that means there is already a aftermarket for the GBA with all kinds of different carts you can use for the DS. Below is a short list of some of the current available carts. Note that older carts needs to be software upgraded before they're NDS hack compatible.
While you can load game backups through PassMe, FlashMe or WifiMe, you still want to be able to save your game progress. This was a bit tricky in the beginning, because the games that you loaded would save directly to the DS game inserted into the DS slot. This severely limited the amount savegames you could carry at any given time. But newer GBA carts has support for patching the location where the savegames are stored, and therfore force the games to save onto the GBA cart instead and let the software on the cart take care of storing and loading seperate savegame files for each individual game that you load from the GBA cart.
Currently the Supercard and the M3 adapter has the best savegame compatibility.
The easiest way to boot applications and games is to get a GBA flash cart. There are handful of different types of carts depending on your requirements and the amount of money you want to spend.
The M3 adapter can use slot-in memory and comes in two models, CompactFlash (CF) and SecureDigital (SD). This is currently the adapter with the best game compatibility, only 3 out of 162 games does not work.
G6Flash comes in three sizes, 1 Gbit (128 MB) , 2 Gbit (256 MB) and 4 Gbit (512 MB). This same company that makes the M3 adapter.
Comes in two models, CompactFlash (CF) and SecureDigital (SD). A PassMe adapter is usually included in the package.
Uses a USB Slim Loader to load files onto the cart. Comes in two models, 512 Mb (64 MB) and 1024 Mb (128 MB). NDS games needs to be patched using the GST program.
Neo MK2/MK3 (MagicKey)
This adapter incorporates SD and MMC slot-in memory in the DS slot instead of the GBA slot. It looks like a PassMe adapter but a bit thicker. Because of this it's not compatible with PassMe, FlashMe or WifiMe.
A new generation flash card. Multi-functional and SDHC Micro-SD based. Real time save, Action Replay, and slow motion function built-in. Comes with USB Micro-SD adapter.
Latest generation flash card. Comes with free slot 2 rumble pack. Supports SHDC Micro-SD cards, Action Replay, and slow motion function. USB Micro-SD adapter included.
Next generation flash card. None of the functions mentioned above. An USB Micro-SD adapter is included. There are many clones floating around.
AceKard 2 is also a next generation flash card. Comes with basic feature set.
- http://forums.maxconsole.net/showthread.php?t=11440 - m3 adapter faq