expansion slots and expansion cards
How to Remove a Computer Expansion Card
A PCIe x1 slot is used to plug in low-demanding PCIe expansion cards that do not have a very high throughput (transfer rate), such as Network Adapters, Port Expansion Cards, Sound Cards, and Certain Riser Cards.
What Are Expansion Slots? - Lifewire
Whether your CPUs, PCIe slots, and expansion cards support PCIe 4.0 speeds is determined by the CPU manufacturer, motherboard manufacturer, and and expansion card manufacturer, respectively.
General Information on PCI, PCI-X and PCI Express Local Bus Technology
PCI slots allow you to install a wide variety of expansion cards including: ... PCI Express supports the same types of expansion cards as PCI and was designed ...