A memory device with modular design and the memory system comprising the same is disclosed. The memory device comprises a substrate plate having a front edge, a rear edge opposite to the front edge, and a top side and a bottom side which are opposite to each other and extend between the front edge and the rear edge; an edge connector positioned at the rear edge and configured to connect to a host connector of a host device; a memory control module positioned on one of the top side and the bottom side of the substrate plate; at least one socket positioned on the top side of the substrate plate and configured to connect to at least one removable memory module; and wherein the memory controller module is electrically coupled to the edge connector and the at least one socket such that the at least one memory module can be accessible by the host device via the memory control module.