What is a PCIe slot?
The size of the PCIe slot needed depends on the specific hardware component being installed and the available PCIe slots on the motherboard.
M.2 PCIe PCI-E Adapter, M.2 to PCI-E3.0 X1 Expansion Card,M2 SSD ...
Is it Possible to Install a PCIe 3.0 NVMe SSD in a PCIe 4.0 M.2 Motherboard Slot?
4 PCI Slot Mid-tower 4th Gen Intel Core Supports Windows 7
4 PCI slot mid-tower PC runs Windows XP, Windows 7 and Windows 10. Also has 3 PCIe slots. Industrial class motherboard for long life and great performance.
Can a Motherboard Bottleneck a GPU? - PC Guide 101
Note: Make sure the GPU PCIe Connector is fully inserted into the PCIe Riser Cable Socket and motherboard PCIe slot when powered off.