A method and a related apparatus for using a dynamic random access memory (DRAM) in substitution of a hard disk drive in a computer system. The computer system has a request format transformation module for transforming a hard disk request signal into a corresponding memory request signal, a memory read/write control circuit for accessing the DRAM, and a memory refresh circuit for periodically refreshing the DRAM to maintain data stored in the DRAM. When the computer system issues the hard disk request signal, the hard disk request signal is transformed into the corresponding memory request signal to access the DRAM instead of a hard disk drive. In addition, when the computer system executes an S4 or S5 state according to the specification of advanced configuration and power interface, the memory refresh circuit will repeatedly refresh the DRAM.