The Sainsmart Uno R3 is a microcontroller board based on the ATmega328 . It has 14 digital input/output pins (of which 6 can be used as PWM outputs), 6 analog inputs, a 16 MHz ceramic resonator, a USB connection, a power jack, an ICSP header, and a reset button. It contains everything needed to support the microcontroller; simply connect it to a computer with a USB cable or power it with a AC-to-DC adapter or battery to get started. 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 with both the board that uses the AVR, which operates with 5V and with the Sainsmart Due that operates 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.
Sainsmart Uno R3 2012 Sainsmart Uno R3 2013 ATmega328 MEGA328P-AU 5V 3.3V-5V (Switch) 7-12V 7-12V 6-20V 6-20V 14 (of which 6 provide PWM output) 14 (of which 6 provide PWM output) 6 8 (Add A6/A7 port) 40 mA 40 mA 50 mA 50 mA 32 KB (ATmega328) of which 0.5 KB used by bootloader 32 KB (ATmega328) of which 0.5 KB used by bootloader 2 KB (ATmega328) 2 KB (ATmega328) 1 KB (ATmega328) 1 KB (ATmega328) 16 MHz 16 MHz
Tips; http://bartruffle.blogspot.no/2013/09/dfu-programming-atmega16u2-on-arduino.html