An embedded multimedia card (eMMC) includes a clock channel receiving a clock from a host, a complementary clock channel receiving a complementary clock from the host, a command/response channel exchanging commands/responses with the host, a plurality of data channels exchanging data between the host and the eMMC, a return clock channel sending a return clock to the host synchronously with data, a complementary return clock channel sending a complementary return clock to the host, and a reference voltage channel that either receives a reference voltage from the host or communicates a reference voltage to the host.