Raspberry Pi 400 Gets an 8GB Upgrade — By Hand-Balling and Soldering a Donor RAM Chip - Hackster.io
Amazon.com: GeeekPi Raspberry Pi CM4 Router Board,Raspberry Pi Compute Module 4 Expansion Board Breakout Board Module for Raspberry Pi Compute Module 4 Series : Electronics
Assembled Gertboard GPIO Expansion Board For Raspberry Pi