The Arduino Uno Rev3 is a microcontroller board based on the ATmega328 (datasheet). It has 14 digital input/output pins (of which 6 can be used as PWM outputs), 6 analog inputs, a 16 MHz crystal oscillator, a USB connection, a power jack, an ICSP header, and a reset button.

It contains everything needed to support the microcontroller; simply connect it to a computer with a USB cable or power it with a AC-to-DC adapter or battery to get started.
The Uno differs from all preceding boards in that it does not use the FTDI USB-to-serial driver chip. Instead, it features the Atmega8U2 programmed as a USB-to-serial converter."Uno" means one in Italian and is named to mark the upcoming release of Arduino 1.0.
The Uno and version 1.0 will be the reference versions of Arduno, moving forward. The Uno is the latest in a series of USB Arduino boards, and the reference model for the Arduino platform.

• Microcontroller ATmega328
  
• Operating Voltage 5V
  
• Input Voltage (recommended) 7-12V
  
• Input Voltage (limits) 6-20V
  
• Digital I/O Pins 14 (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 of which 0.5 KB used by bootloader
  
• SRAM 2 KB
  
• EEPROM 1 KB
  
• Clock Speed 16 MHz