Arduino Micro Pro R3
The Arduino Micro is essentially a shrunk-down (1.9″ × 0.7″) version of the Arduino Leonardo: it is a microcontroller board based on the ATmega32U4 running at 16 MHz with 24 digital input/output pins (of which 7 can be used as PWM outputs and 12 as analog inputs). This board ships with the male header pins soldered in.
The Arduino Micro is a microcontroller board based on the ATmega32U4, developed in conjunction with Adafruit. It has 24 digital input/output pins (of which 7 can be used as PWM outputs and 12 as analog inputs), a 16 MHz crystal oscillator, a micro USB connector, an in-circuit system programming (ICSP) header, and a reset button.
It contains everything needed to support the microcontroller; simply connect it to a computer (or appropriate wall power adapter) with a Micro USB cable (not included) to get started. The headers are arranged with a 0.1″ spacing for compatibility with standard solderless breadboards and perfboards and connectors that use a 0.1″ grid.
The Arduino Micro features a user-programmable ATmega32U4 AVR microcontroller that has built-in USB functionality, eliminating the need for a secondary processor or serial adapter. This makes the Arduino Micro more versatile: in addition to supporting a virtual (CDC) serial/COM port interface, it can appear to a connected computer as a mouse and keyboard. See Arduino’s getting started page for more implications of the Arduino Micro’s single-MCU design.