[nextparadigms]

If this is the first ARM-based Arduino, what was the Arduino chip based on that Google used at I/O for that accessory API thing? Was it a regular (but smaller) Arduino?

[jmaygarden]

All of the official Arduino hardware designs have used an AVR to the best of my knowledge. Netduino [1] is a related project that runs a stripped down .NET framework on an ARM7 core. However, that's not what Google used. It may be the reference for Windows Phone add-ons.

[1] http://netduino.com/

[raphman]

probably a 'regular' Arduino, i.e. an 8-bit AVR microcontroller.

See http://www.arduino.cc/en/Main/ArduinoBoardADK and http://www.amarino-toolkit.net/

[nemik]

It uses an ATmega2560. Still an 8-bit AVR but has more memory and USB host functionality.