There are two versions of Arduino UNO R3 currently available:
- Arduino UNO R3
- Arduino UNO R3 SMD
The difference between the two comes down to the AVR chip package used. In the UNO SMD (Surface Mounted Device) the microprocessor chip (ATmega328) is integrated and soldered onto the board; while in the standard UNO, the ATmega328 is DIP (Dual In-line Packaged), which means that the microprocessor chip can easily be removed and replaced if necessary. This is very convenient if the chip gets damaged, or if you want to use the chip for a standalone project.