PCIe slots are different from one another in terms of their capabilities and usage. They come in a variety of shapes and sizes, and have different numbers of PCIe lanes.
The number of lanes refers to the number of connections that can be made from the slot to the motherboard. .
There are six PCIe slots on a motherboard: three on the north side of the board, and three on the south side. The first two PCIe slots are x16 slots, which means they can support four PCIe graphics cards or two dual-width PCIe cards. The next slot is x8, which can support two graphics cards or one dual-width card and one regular PCIe card. The third slot is x4, which can support one graphics card or one regular PCIe card and one dual-width PCIe card.
The fourth and fifth slots are x2, which can support either a regular or dual-width PCIe card. The sixth slot is x1, which is only used for connecting a keyboard or mouse to the computer.