How many PCIe card sizes exist today, and where are they used?

Perhaps use open-ended PCIe x1 slots instead of PCIe x16 slots? #9 pcie x1 in x16 slot For example, you can fit a PCIe x1 card in a PCIe x16 slot However, you can't do the opposite You can mount, for instance, a PCIe x1 sound pcie expansion slot For example, many high-end boards use x16 slots only to maximize performance for full-sized expansion cards So, what if you want to use a PCIe x1 peripheral,

pcie 20 x16 slot I see various mobos with, for example, 'half-length' PCIe x16 slots But this is a contradiction in terms A PCIe x16 slot by definition is