Official Raspberry Pi Page
Key Differences To The Raspberry Pi 2
1.2GHz 64-bit quad-core ARMv8 CPU (BCM2837)
Built in 802.11n Wireless LAN
Built in Bluetooth 4.1 and Bluetooth Low Energy (BLE)
Software difference issues we’ve encountered:
UART for Pre RPi3 is “/dev/ttyAMA0”. On the RPi 3 this is assigned to bluetooth and the UART is now “/dev/ttyS0”.
Shared Specifications To The Raspberry Pi 2
Identical form factor to the RPi 2, RPi1 Model B+.
Complete compatibility with Raspberry Pi 1 and 2.
4 USB ports
40 GPIO pins
Full HDMI port
Combined 3.5mm audio jack and composite video
Camera interface (CSI)
Display interface (DSI)
Micro SD card slot
VideoCore IV 3D graphics core