The Pi 400 is a Raspberry Pi built into a 78 or 79-key Keyboard depending on the region with the following features
The processor is the Broadcom BCM2711, Quad-Core 64-bit SoC (Arm Cortex-A72 @ 1.8GHz)
The memory RAM included is 4GB LPDDR4-3200
The connectivity options are wireless LAN (Dual-Band 2.4Ghz and 5.0Ghz) IEEE 802.11 B/G/N/AC Bluetooth 5.1, BLE
Gigabit Ethernet
1 x 40 pin GPIO Header
1 x MicroSD Card Slot
2 x Micro HDMI Connections
1 x USB-C Connector for 5V Power
2 x USB 3.0
1 x USB 2.0
1 x Ethernet connector
Other HDMI-A Male to Micro HDMI-D Male Cable options can be found here, https://www.digikey.com/short/4c32db
1690-RPIUSB-CPOWERSUPPLYBLACKUS-ND
Other USB-C adapter options https://www.digikey.com/short/4c321q
You can use a wired mouse such as
Wireless Mouse options here https://www.digikey.com/short/4c3dvp
I tested the Pi 400 out with the Chromium OS found here Releases · FydeOS/chromium_os-raspberry_pi · GitHub with the image file name chromiumos_image_r86r2-rpi4b.img.xz . If you plan on testing this OS with the Pi, just download the img file and upload with the Raspberry Pi Imager found here Introducing Raspberry Pi Imager, our new imaging utility - Raspberry Pi. In the Raspberry Pi Imager select “Use Custom” under Operating System then find the Chromium OS image in the downloads folder then write that file to the microsd card as seen below.
Applicable part numbers
SC0372,
SC0373, SC0376, SC0374, SC0375, SC0377
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Raspberry Pi boards - FAQs - Engineering and Component Solution Forum - TechForum │ Digi-Key