The Raspberry Pi Model B line is a desktop computer in a package the size of a credit card. All you need to do is plug in a monitor, keyboard, mouse and load the latest Raspbian image onto a MicroSD Card and you have a full desktop computer solution. Projects like Tensorflow, PiHole, Minecraft, and Kodi make it an excellent tool for a multitude of uses.
The RPi4 retains a lot of the features of the RPi3 B+ including the pin-out for the 40 pin header. Wireless is still available on the 4 in the form of dual-band 2.4/5.0 GHz WiFi and Bluetooth 5.0. A new feature on the 4 is the inclusion of a USB Type-C connector for power delivery replacing the Mini-B connector.

Specifications
Broadcom BCM2711, Quad core Cortex-A72 (ARM v8) 64-bit SoC @ 1.5GHz
1GB, 2GB or 4GB LPDDR4-3200 SDRAM (depending on model)
2.4 GHz and 5.0 GHz IEEE 802.11ac wireless, Bluetooth 5.0, BLE
Gigabit Ethernet
2 USB 3.0 ports; 2 USB 2.0 ports.
Raspberry Pi standard 40 pin GPIO header (fully backwards compatible with previous boards)
2 × micro-HDMI ports (up to 4kp60 supported)
2-lane MIPI DSI display port
2-lane MIPI CSI camera port
4-pole stereo audio and composite video port
H.265 (4kp60 decode), H264 (1080p60 decode, 1080p30 encode)
OpenGL ES 3.0 graphics
Micro-SD card slot for loading operating system and data storage
5V DC via USB-C connector (minimum 3A*)
5V DC via GPIO header (minimum 3A*)
Power over Ethernet (PoE) enabled (requires separate PoE HAT)
Operating temperature: 0 – 50 degrees C ambient
* A good quality 2.5A power supply can be used if downstream USB peripherals consume less than 500mA in total.
 
The Raspberry Pi 4 does have the ability to consume more power than the Pi 3 B+, so a proper power supply will be needed. Power over Ethernet (PoE) is available with the use of the PoE HAT (see related products). Those looking to use third party power supplies and cables or to run more intensive programs on the Pi; a proper source of power and heat dissipation measures are recommended.