The Yún is unique in the Arduino lineup, as it has a lightweight Linux distribution to complement the traditional microcontroller interface. It also has WiFi and Ethernet connections on board, enabling it to communicate with networks out of the box. The Yún’s Linux and Arduino processors communicate through the Bridge library, allowing Arduino sketches to send commands to the command line interface of Linux.
The Arduino Yún has the same footprint as an Arduino Uno but combines an ATmega32U4 microcontroller (the same as the Leonardo) and a Linux system based on the Atheros AR9331 chipset. Additionally, there are built-in Ethernet and WiFi capabilities. The combination of the classic Arduino programming experience and advanced internet capabilities afforded by a Linux system make the Yún a powerful tool for communicating with the internet of things.
The Yún’s layout keeps the I/O pins the same as the Arduino Leonardo. As such, the Yún is compatible with the most shields designed for Arduino.
With the Yún’s auto-discovery system, your computer can recognize boards connected to the same network. This enables you to upload sketches wirelessly to the Yún. You can still upload sketches to the Yún through the micro-USB connector just as you would with the Leonardo.
The Yún has two separate network interfaces, a 10/100 Mbit/s Fast Ethernet port and a IEEE 802.11 b/g/n standard compliant 2.4GHz WiFi interface, supporting WEP, WPA and WPA2 encryption. The WiFi interface can also operate as an access point (AP). In AP mode any WiFi enabled device can connect directly to the network created on the Yún. While a Yún in this mode can’t connect to the internet, it could act as a hub for a group of WiFi enabled sensors.
For more detail: Let’s explore Arduino Yún’s unique features – Hardware review