The D1 Mini Pro microcontroller is based on the WiFi-SoC ESP8266EX and is made for fast Internet-of-Things (IoT) prototyping. It offers the convenience of a micro-USB connection for both power and data (running at 3.3V), and despite its size has built-in WiFi with an external antenna for greater transmission distances, and 16MB of flash memory.
The development board is based on the WiFi-SoC ESP8266EX and is made for fast Internet-of-Things (IoT) prototyping. It is flashed with the NodeMCU firmware and can be set up and programmed right away with the onboard micro-USB connection. With only a few lines of code, the NodeMCU Dev Kit is connected to your local network and ready to be controlled by other network members like computers and smartphones.
Features and Specifications:
Microcontroller: ESP-8266EX
Operating Voltage: 3.3V Max (5V power from MicroUSB connector is internally converted to 3.3V)
Digital I/O Pins: 11, all pins have interrupt/PWMI2C/one-wire support except D0
Analog Input: 1 (3.2V max input)
Connector: MicroUSB
Clock Speed: 80MHz/160MHz
Flash: 16M bytes
USB Interface: CP2104 USB-TO-UART IC
Antenna:  Built-in ceramic antenna and connector for external U.FL antenna (included)
Dimensions: 34mm x 25.5mm x 3.6mm excluding antenna
Weight: Approx. 2.5g excluding connectors and external antenna
Same dimensions as D1 Mini, but lighter
Compared to the D1 Mini, the D1 Mini Pro offers: 
Flash: 16M bytes (128M bits) in the D1 Mini Pro vs 4M bytes (32M bit) in the D1 Mini
USB-TO-UART IC: CP2104 vs CH340G
Built-in ceramic antenna or external antenna vs PCB antenna in the D1 Mini
Weight: 2.5g vs 3.9g
Thickness: 3.6mm vs 6.7mm