This is Due AT91SAM3X8E ARM Cortex-M3 Board 84MHz 512KB Board compatible with Arduino.

The Due is a microcontroller board based on the Atmel SAM3X8E ARM Cortex-M3 CPU. The Due Arduino AT91SAM3X8E ARM Cortex-M3 Board is the first Arduino board based on a 32-bit ARM core microcontroller. It has 54 digital input / output pins (of which 12 can be used as PWM outputs), 12 analog inputs, 4 UARTs (hardware serial ports), a 84 MHz clock, an USB OTG capable connection, 2 DAC (digital to analog), 2 TWI, a power jack, an SPI header, a JTAG header, a reset button and an erase button.

The board contains everything needed to support the microcontroller; simply connect it to a computer with a micro-USB cable or power it with an AC-to-DC adapter or battery to get started. The Due is compatible with all Arduino shields that work at 3.3V and are compliant with the 1.0 Arduino pinout.

The SAM3X has 512KB (2 blocks of 256KB) of flash memory for storing code. The bootloader is pre-burned in a factory from Atmel and is stored in a dedicated ROM memory. The available SRAM is 96KB in two contiguous banks of 64KB and 32KB. All the available memory (Flash, RAM, and ROM) can be accessed directly as a flat addressing space.

It is possible to erase the Flash memory of the SAM3X with the onboard erase button. This will remove the currently loaded sketch from the MCU. To erase, press and hold the Erase button for a few seconds while the board is powered.

Due follows the 1.0 pinout:

TWI: SDA and SCL pins that are near to the AREF pin.
The IOREF pin which allows an attached shield with the proper configuration to adapt to the voltage provided by the board. This enables shield compatibility with a 3.3V board like the Due and AVR-based boards which operate at 5V.
An unconnected pin, reserved for future use

Connections / Interfaces

Digital I / O pins: 54
With PWM: 12
USB: Yes
SPI: No
I²C: No
ICSP: Yes
TWI: 2x
UART: 4x
CAN: Yes
SAC: 2x
LAN: No
Bluetooth: No

The Due has it’s own, dedicated forum for discussing the board. The link is in the Attachments and Links.

Note: Unlike other Arduino boards, the Due board runs at 3.3V. The maximum voltage that the I/O pins can tolerate is 3.3V. Providing higher voltages, like 5V to an I/O pin could damage the board. 

Features :

1. A 32-bit core, that allows operations on 4 bytes wide data within a single CPU clock.
2. CPU clock at 84Mhz
3. 96KBytes of SRAM
4. 512KBytes of flash memory for code
5. A DMA controller, that can relieve the CPU from doing memory intensive tasks.

Specifications:

Package Includes :

1 x Due AT91SAM3X8E ARM Cortex-M3 Board 84MHz 512KB Board.

Useful Links :

Due Forum Link

Getting started with the Due Arduino

https://www.keil.com/dd/chip/5412.htm#:~:text=The%20Atmel%20SAM3X8E%20is%20a,bank%20%2D%20From%2032%20to%20100