Arduino Nano is an Arduino board based on ATmega328 (Arduino Nano 3.x). It is functionally identical to the UNO, but smaller and has a breadboard-friendly footprint. It works with a Mini-B USB cable instead of a DC power jack for the external power source. It also has more or less the same electrical functionality of the Arduino Duemilanove with more analog input pins and onboard +5V AREF jumper.
The Arduino Nano can be powered via the Mini-B USB connection, 6-20V unregulated external power supply (pin 30), or 5V regulated external power supply (pin 27). The power source is automatically sensed and selected to the highest voltage source.
Header pins are unsoldered and require the user to solder if required.