are pcie slots backwards compatible: How PCI Express Works | HowStuffWorks. PCIe Slots & Lanes Explained: Choosing the Right Connection (Fast ... . Which PCIe Slot is best for your Graphics Card? - CGDirector.
PCI slots are an integral part of a computer's architecture, but they have some shortcomings. Fortunately, PCI Express (known as PCIe) provides more bandwidth and is compatible with existing operating systems. Find out how PCIe works!
For example,
PCIe X16 slot can be compatible with X4 or X8 products. But short
slots cannot be compatible with long interface products because they cannot be inserted.
To determine which graphics cards are compatible with your motherboard, check its
slot type (usually PCIe), power supply capacity, and physical space in the case.