1. A memory device, comprising: a first memory configured to have a first storage capacity; a second memory configured to have a second storage capacity greater than the first storage capacity; and a controller configured to receive a virtual address from an external host and configured to provide the external host with an address space corresponding to a third storage capacity, the third storage capacity being less than a sum of the first storage capacity and second storage capacity, wherein the controller converts and translates the virtual address into a physical address of either the first or second memory based on a temporal locality of the received virtual address, where data requested from the external host is stored in the first memory, the controller transmits the requested data from the first memory to the external host, and where the requested data is not stored in the first memory, the controller transmits the requested data from the second memory to the external host.