Everything You Need to Know About PCIe 4.0 - trentonsystems.com
This was all about the Expansion cards and the expansion slots which are used to enhance the performance of the the computer system.
Do B450 Motherboads support PCI-E 4.0? - AMD Community
cards are devices that fit into the PCIe slot on your computer motherboard, providing additional functionality or enhancing existing computer features. ...
Echo III Rackmount (Thunderbolt to PCIe Card Expansion System ...
Computers have expansion slots on the motherboard to install adapter cards. The type of adapter card connector must match the expansion slot.