A file system is capable of reading and writing a large amount of stream data, such as digital video/audio data, in real time, and is also capable of efficiently dealing with a normal data file of a small size. In the file system, realtime stream data is recorded in a recording apparatus while dividing the data into data units, each data unit corresponding to a predetermined time interval and being composed of a series of blocks, so as to form a realtime data file. When the realtime data file is read in real time, the data stored in the series of blocks is read at one time. Whether the data can be recorded or read is determined in accordance with a schedule of a recording/reading process of other realtime data or non-realtime data. The data is recorded or read in accordance with the determination result.