Can I install DDR3L RAM in a laptop which supports DDR3 ...
It states that "you cannot put DDR3 in a DDR3L slot" because it can only operate at 1.5v and not 1.35v. It also states that you can put "DDR3L in a DDR3 slot" because DDR3L can operate at 1.35v and 1.5v.
Mainboard Gigabyte -Intel H610- LGA1700(12+13+14th); 2 slot :DDR ...
So, in this case, if you were to install a PCIe 3.0 device on a PCIe 2.0 slot, it would work, but the slot can be a bottleneck.
What Are PCIe Slots And How Can I Use Them in My PC
You can insert a PCIe x1 card into a PCIe x16 slot, but that card will receive less bandwidth. Similarly, you can insert a PCIe x8 card into a PCIe x4 slot, but it’ll only work with half the bandwidth compared to if it was in a PCIe x8 slot.