The invention provides a master MMC/SD apparatus for simultaneously supporting bulk storage and Ethernet communication, a slave MMC/SD apparatus for simultaneously supporting bulk storage and Ethernet communication, a system composed of these two apparatuses as well as a method of operating the system. The apparatuses, system and method which simultaneously support bulk storage and Ethernet communication and which are based on MMC/SD interface enable a master apparatus with MMC/SD interface to support network function while maintaining bulk storage function as well, thus greatly expanding applicable areas of such embedded terminal apparatus with the MMC/SD interface that has bulk storage function.