Arduino is an open-source physical computing platform based on a simple i/o board and a development environment that implements theProcessing/Wiring language. Arduino can be used to develop stand-alone interactive objects or can be connected to software on your computer (e.g. Flash, Processing, MaxMSP). The open-source IDE can bedownloaded for free (currently for Mac OS X, Windows, and Linux).
Arduino Yun is the first member of a new groundbreaking line of WiFi products combining the power Linux with ease of use of Arduino. The first Arduino Yun is the combination of a classic Arduino Leonardo (based on the Atmega32U4 processor) with a WiFi system-ona-chip running Linino (a MIPS GNU/Linux based on OpenWRT). Arduino embedded the Linux machine directly on the PCB of the Arduino Leonardo and connected the two so that from Arduino it’s very easy to run commands on the Linux side and use it as an Ethernet and WiFi interface.
The board has built-in Ethernet and WiFi support, a USB-A port, micro-SD card slot, 20 digital input/output pins (of which 7 can be used as PWM outputs and 12 as analog inputs), a 16 MHz crystal oscillator, a micro USB connection, an ICSP header, and a 3 reset buttons.
Note: The Arduino PoE module will not work with this board. A YUN-specific module will be coming out. In the meantime, just leave this unpopulated