Everything You Need to Know About an ATX Motherboard
The documentation should provide a list of the types of expansion slots available, while physically inspecting the motherboard can help you identify the specific slots available.
Solved: M.2 Slots for Motherboard 8860 A(SMVB)
The 8860 A(SMVB) motherboard specifications list it as having two M.2 expansion slots. HP Desktop PCs - Motherboard Specifications, Stark | HP® Customer Support Looking at the motherboard, I'm only able to find one.
Which PCIe Slot is best for your Graphics Card? - CGDirector
The width of a graphics card is often expressed in terms of "slots," which indicates how many expansion slots it occupies on a motherboard.