With one of latest Broadcom 2711; Quad-Core Cortex A72 (ARM V8-A) 64-bit SoC Clocked at 1.5GHz processor improved power consumption; and thermals on the Pi 4 B means that the CPU on the BCM2837 SoC can now run at 1.5 GHz; a 20% increase on the previous Pi 3 model (which ran at 1.2GHz).
Video performance on Pi 4 B is upgraded with dual-display support at resolutions up to 4K via a pair of micro-HDMI ports; hardware video decode at up to 4Kp60 which supports H 265 Decode (4Kp60); H.264, and MPEG-4 decode (1080p60).
A significant change on the Pi 4 B compared to the previous Pi 3 models is the inclusion of a new faster; dual-band wireless chip with 802.11 b/g/n/ac wireless LAN.
The dual-band 2.4GHz and 5GHz wireless LAN enables faster networking with less interference and the new PCB antenna technology allow better reception.
Latest 5.0 Bluetooth allows you to use a wireless keyboard/trackpad with more range than before without extra dongles; keeping things nice and tidy.
Enhanced Ethernet Connectivity:
The Pi 4 B has significantly faster-wired networking with USB 3.0 technology; thanks to an upgraded USB/LAN chip; and you should see speeds that are 10x faster than on previous models of the Pi.
The GPIO header remains the same, with 40 pins; fully backwards-compatible with previous boards as on the previous three models of Pi. However; it should note that the new PoE header pins may contact components on the underside of some HATs; like Rainbow HAT. Some standoffs will prevent any mischief from occurring though!