This official Arduino Pro Mini was designed to minimal circuit of Arduino. This is a 3.3V/5V Arduino running the 16MHz bootloader (select 'Arduino Duemilanove w/ 328' within the Arduino software). Arduino Pro Mini does not come with connectors populated so that you can solder in the provided pin headers or any other connectors/wires at any orientation you need. This is good if your project have limited space and you are familiar with Arduino. We recommend first time Arduino users start with the Uno R3. It's 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.

This board is really lower the cost of an Arduino. The Arduino Pro Mini is like the Arduino Mini (same pin out) but to keep the cost low, all SMD components are used, made it two layer, etc. This board connects directly to the UC00B and supports auto-reset. 

Features:

• ATmega328 running at 16MHz with external resonator (0.5% tolerance)
• USB connection off board
• Supports auto-reset
• 3.3V/5V regulator
• Max 150mA output
• Over current protected
• Reverse polarity protected
• DC input 5V up to 12V
• On board Power and Status LEDs
• Dimensions: 0.7" x 1.3" (18mm x 33mm)
• Weight: < 2 grams

Packing List:

• 1x Arduino Pro Mini
• Pin headers

Useful Links:

• Arduino Pro Mini Home Page 
• Getting Started Tutorial