Raspberry Pi 4 Model B Kit 2GB 4GB 8GB RAM + Card + Case + Cooling Fan + 4K HD Video Cable + Power Supply for Raspberry Pi 4 B|Demo Board| - AliExpress
What's the physical difference between 4 GB RAM and 8 GB RAM? What are they made of? How does it work? - Quora
Why you should upgrade from 4GB to 8GB RAM - Dove Computer Solutions Ltd