This is a 5V Arduino running the 16MHz bootloader. Arduino Pro Mini does not come with connectors populated so that you can solder in any connector or wire with any orientation you need. We recommend first time Arduino users start with the Uno R3. It is a great board that will get you up and running quickly. The Arduino Pro series is meant for users that understand the limitations of system voltage (5V), lack of connectors, and USB off board. We really wanted to minimize the cost of an Arduino. In order to accomplish this we used all SMD components, made it two layer, etc. There is a voltage regulator on board so it can accept voltage up to 12VDC. If you are supplying unregulated power to the board, be sure to connect to the "RAW" pin and not VCC.
ATmega328 running at 16MHz with external resonator (0.5% tolerance)
No USB connection off board. Need FTDI board (or similar device) to program.