Solid-state drive
When SSDs were first introduced into the market, manufacturers' made sure that they fit into the slots and bays initially used by the HDDs. As such, they had the 3.5 and 2.5 inch form factors. However, as technology advances, more form factors emerged. Smaller form factors that directly interfaces with PCIe and NVMe slots emerged. These included the mSATA, PCIe and M.2, form factors.