Arduino Nano is a surface mount breadboard embedded version with integrated USB. It is a smallest, complete, and breadboard friendly. It has everything that Diecimila/Duemilanove has (electrically) with more analog input pins and onboard +5V AREF jumper. Physically, it is missing power jack. The Nano is automatically sense and switch to the higher potential source of power, there is no need for the power select jumper.
Nano’s got the breadboard-ability of the Boarduino and the Mini+USB with smaller footprint than either, so users have more breadboard space. It’s got a pin layout that works well with the Mini or the Basic Stamp (TX, RX, ATN, GND on one top, power and ground on the other).
Automatic reset during program download
Power OK blue LED
Green (TX), red (RX) and orange (L) LED
Auto sensing/switching power input
Small mini-B USB for programming and serial monitor
ICSP header for direct program download
Standard 0.1” spacing DIP (breadboard friendly)
Manual reset switch
Microcontroller : Atmel ATmega 328
Operating Voltage(logic level) : 5V
Input Voltage (recommended) : 7-12 V
Input Voltage (limits) : 6-20 V
Digital I/O Pins : 14 (of which 6 provide PWM output)
Flash Memory : 32 KB (of which 2KB used by bootloader)