Raspberry Pi 4
The Raspberry Pi 4 is the 4th generation of the mainline series of Raspberry Pi single-board computers. Developed by Raspberry Pi Trading and released on 24 June 2019, the Pi 4 came with many improvements over its predecessor; the SoC was upgraded to the Broadcom BCM2711, two of the Raspberry Pi's four USB ports were upgraded to USB 3.0, and options were added for RAM capacities larger than the 1 GB standard for the preceding Raspberry Pi 3 series. The Pi 4 also ends the trend of the $35 maximum MSRP that previous Raspberry Pis had adhered to, as the larger RAM capacities added extra cost to the board; however, the base 1 GB model is still sold for $35. On 28 September 2023, the Raspberry Pi 5 was announced as the successor to the Raspberry Pi 4.
The Raspberry Pi 4 is the 4th generation of the mainline series of Raspberry Pi single-board computers. Developed by Raspberry Pi Trading and released on 24 June 2019, the Pi 4 came with many improvements over its predecessor; the SoC was upgraded to the Broadcom BCM2711, two of the Raspberry Pi's four USB ports were upgraded to USB 3.0, and options were added for RAM capacities larger than the 1 GB standard for the preceding Raspberry Pi 3 series. The Pi 4 also ends the trend of the $35 maximum MSRP that previous Raspberry Pis had adhered to, as the larger RAM capacities added extra cost to the board; however, the base 1 GB model is still sold for $35. On 28 September 2023, the Raspberry Pi 5 was announced as the successor to the Raspberry Pi 4.

Features
CPU
The Raspberry Pi 4 uses a Quad-core ARM Cortex-A72 clocked at either 1.5 GHz or 1.8 GHz depending on the revision of the BCM2711 SoC on the board. The older B0 stepping was originally used for the Pi 4, but this was replaced with the newer C0-stepped chip starting in mid-2021. The higher clock rate of the C0 stepping is due to the marginally improved thermals. The processor also contains 32 KB of data L1 cache and 48 KB of instruction L1 cache, alongside 1 MB of shared L2 cache.

GPU
The Broadcom BCM2711 SoC features an upgraded GPU compared to previous iterations of Raspberry Pi, going from the VideoCore IV clocked at 400 MHz to the VideoCore VI clocked at 500 MHz. Alongside the faster clock rate, the VideoCore VI also includes its own memory manager, allowing it to access more memory than its predecessor.The VideoCore VI is compliant with OpenGL ES 3.1 and Vulkan 1.2.

RAM
The Raspberry Pi 4 replaces the 1 GB of LPDDR2 with options for either 1 GB, 2 GB, 4 GB, or 8 GB of 3200 MHz LPDDR4. The 8 GB Pi 4 released a year after the other models.

IO and Connectivity
Numerous improvements were introduced to IO functionality with the Raspberry Pi 4. The total USB bandwidth was upgraded, going from four USB 2.0 ports to two USB 3.0 ports and 2 USB 2.0 ports. A dedicated ethernet controller on the BCM2711 SoC allowed for the addition of gigabit ethernet. The singular full-sized HDMI port on the Raspberry Pi 3 has also been replaced with dual micro-HDMI connectors.Bluetooth was upgraded from 4.2 on the Raspberry Pi 3, to 5.0 on the Raspberry Pi 4.The power supply connector also changed from Micro-USB to USB-C. The ethernet port features Power over Ethernet IEEE 802.3af (802.3at Type 1) like the Raspberry Pi 3 Model B+.

Compute Module 4
On 19 October 2020, 16 months after the original release of the Raspberry Pi 4 Model B, Raspberry Pi released the Compute Module 4, a version of the Pi 4 platform designed for embedded and industrial applications. The Compute Module 4, like the original Pi 4 model, features options for 1 GB, 2 GB, 4 GB, and 8 GB of RAM; however, it also features options for 8 GB, 16 GB, or 32 GB of optional eMMC onboard storage. There is also an option for wireless 2.4/5 GHz wireless connectivity. Because of the total of 32 variations for the Compute Module 4, the MSRP ranges from $30 to $95 depending on the configuration.

IO and Connectivity
Unlike the original Raspberry Pi 4 Model B, the Compute Module 4 uses a pair of 100-pin connectors on the bottom of the board for IO instead of traditional ports. These connectors are not meant to be accessed directly by the end user; instead, they are meant to interface with a daughter board to provide IO functionality. While the pins on the Compute Module 4 can be used for the same interfaces as other Pi 4 models, the Compute Module 4 exposes the PCIe 2.0 bus that was previously used for USB 3.0. The freeing of the PCIe bus allows designers to use it for other use cases, such as native NVMe storage or faster networking.Models of Compute Module 4 that have an eMMC chip do not have the capability to connect to external eMMC or microSD storage.

Raspberry Pi 400
The Raspberry Pi 400 is the final Raspberry Pi product to be based on the Raspberry Pi 4 platform. Released 2 November 2020, the Pi 400 is a Raspberry Pi 4 with 4 GB of RAM in a keyboard form factor. Intended to be used as a desktop PC, the Raspberry Pi 400 can either be bought alone for $70, or as part of a desktop kit which includes the Pi 400 itself, a power supply, a mouse, a 16 GB microSD card with Raspberry Pi OS preinstalled, and a guide book for $100.

Peripherals
Compute Module 4 IO Board
The Compute Module 4 IO Board is an official daughter board designed to give Compute Module 4 users easier access to its various interfaces. While the board does feature many of the same ports as the original Pi 4 Model B, the Compute Module 4 IO Board also adds and changes various connectivity options.

PCI-e 2.0
The CM4 IO Board exposes the PCI-e 2.0 bus of the Compute Module 4, rather than having the bus directly connect to a USB 3.0 controller. The bus is exposed through a standard 1x PCI-e connector, allowing for the connection of standard PCI-e peripherals such as networking cards, high-speed storage devices, and even allows the possibility of external GPU support.

USB-C Power Issues
During the launch of the original Raspberry Pi 4, people soon discovered that some USB-C power cables would not work with the board. The reason for this was found to be the Pi 4's USB-C power connector being non-compliant with the official specification. The issue stems from the Raspberry Pi 4's use of a shared CC pull-down resistor, rather than each CC line being given its own resistor; the result of this change is that chargers using an e-marker chip will not be able to detect the Pi, thus supplying no voltage.The USB-C implementation was fixed with the release of the 1.2 revision of Raspberry Pi 4, which allowed for high-speed USB-C cables to work with the board.


== References ==