Curiosità, i primi due piedini in alto a sx ed il primo piedino in basso a sx, a cosa servono ? Non ho trovato niente in merito
http://arduino.cc/en/Main/ArduinoBoardUno:
Revision 3 of the board has the following new features:1.0 pinout: added SDA and SCL pins that are near to the AREF pin and two other new pins placed near to the RESET pin, the IOREF that allow the shields to adapt to the voltage provided from the board. In future, shields will be compatible both with the board that use the AVR, which operate with 5V and with the Arduino Due that operate with 3.3V. The second one is a not connected pin, that is reserved for future purposes.
Stronger RESET circuit.
Atmega 16U2 replace the 8U2.
Ciao Uwe