Fully compatible with Arduino. This is a 5V 16MHz bootloader. 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 users start with the Duemilanove. It’s a great board that will get you up and running quickly. The Pro series is meant for users that understand the limitations of system voltage (5V), lack of connectors, and USB off board. The Pro Mini is like the Mini (same pin out) but to keep the cost low, using all SMD components, with 2 layers, etc. This board connects directly to the FTDI Basic Breakout board and supports auto-reset. The Pro Mini also works with the FTDI cable but the FTDI cable does not bring out the DTR pin so the auto-reset feature will not work.