How does the Nintendo 3DS play DS games?

Games for the original Nintendo DS run, and have always run, on Nintendo 3DS hardware. I've been trying to read about how this works but am not really finding anything definitive.

How does the Nintendo 3DS play and run DS games?

• Does the 3DS include a DS "System on a Chip" a la Playstation consoles?
• Does the 3DS architecture natively support DS code?
• Does the 3DS use software emulation to run DS games?

To be clear, I'm not asking for technical support with my 3DS. I'm also not asking about any homebrew setups here, but just about Nintendo's official operating system and firmware for the 3DS.

Solution 1:

This is not emulation, many of the NDS components are present in the 3DS exclusively to run DS games. The 5 - 8 sec black screen when launching an NDS game is there because the console starts the dedicated "NDS processor" inside, and adapts the game resolution to the 3DS screen.

Between the DS and the 3DS, the so-called "game components" have not evolved much in terms of function, so many of the components are compatible between the two consoles.

We can say that the 3DS has a half of DS inside itself, and the 3DS part of the console fills the other half.