A system of recording or reading data are discussed. According to an embodiment, the system includes: a host device transmitting a write or read command and data to be written or receiving data based on the read command; and a recording/reproducing device, operatively coupled to the host device via interface, controlling a write or read operation in response to the write or read command the from the host device. The recording/reproducing device includes, a pickup for writing or reading data to or from medium, and a controller for determining whether the data requires a real time recording or producing, controlling a recording or reading operation such that a defective block is replaced with a spare block of the spare area, based upon the determination.