When receiving request commands from different hosts, a data system generates corresponding phase control signals and access signals based on the formats of each request command. Based on the phase control signals, timing signals corresponding to respect request commands and including a plurality of enabling time slots are generated in a way that only one timing signal includes an enabling time slot at a certain point of time. Next, an access control signal is outputted to a storage device during the enabling time slot of a corresponding timing signal. Therefore, the storage device only needs to respond to one request command at a certain point of time, and multiple data access can be effectively controlled in the data system.