Description:
The Arduino Uno is a microcontroller board based on a removable, Dual-Inline-Package (DIP) ATmega328 AVR microcontroller. It has 20 digital input/output pins (6 of which can be used as PWM outputs and 6 as analog inputs), a 16 MHz resonator, a USB connection, a power jack, an In-Circuit System Programming (ICSP) header, and a reset button. The Arduino has an extensive support community which makes it a very easy way to get started working with embedded electronics.

New for R3:

•     Atmega8U2 replaced with Atmega16U2
•     Reset Button moved to the edge of board
•     SDA and SCL pins added next to AREF

Check out our starter kit: JS Arduino Starter Kit (Beginner)

Features:

•     Microcontroller: ATmega328
•     Operating voltage: 5 V
•     Input voltage (recommended): 7-12 V
•     Digital I/O pins: 20 (of which 6 provide PWM output)
•     Analog input pins: 6*
•     DC current per I/O pin: 40 mA
•     DC current for 3.3V pin: 50 mA
•     Flash memory: 32 KB (ATmega328)
•     SRAM: 2 KB (ATmega328)
•     EEPROM: 1 KB (ATmega328)
•     Clock speed: 16 MHz

Documents:
Arduino Home Page