Memory device, refresh method, and system including the same

A refresh method comprising the steps of:

• mapping a virtual address to a physical address in a table of a memory management unit, loading a specific bit of the physical address;
• extracting a row address information for performing a refresh operation for only an area, in which a program is executed, from the physical address;
• setting a signal for masking the refresh operation of a memory device in a mode register set of the memory device;
• outputting a refresh command signal and an address in response to the row address information applied from the memory management unit;
• controlling a refresh signal in response to the refresh command signal and a refresh skip signal for masking the refresh operation;
• performing the refresh operation in response to the refresh command signal, the address applied from a memory controller and the refresh skip signal for only a used memory area in correspondence to the row address information and a refresh signal set in the mode register set when a refresh management mode is entered;
• releasing the refresh management mode;
• and
• resetting the mode register set in response to an active signal and an external address.