Abstract: A method of inputting and outputting information files between a computer memory and a write-once medium in which a cache memory is established as an intermediary between an operating system's transfer address and the medium. The cache includes a system file allocation structure in a format corresponding to that for erasable media and a media directory file area. The directory in the write-once medium is read to the cache and the system file allocation structure is constructed from the directory information. When performing an operating system command, such as a read or write, access to the medium is made via the cache memory. For example, when reading a data file, sector locations indicated by the system file allocation structure are first mapped to corresponding sectors in the medium directory file area and the corresponding sectors are read from the medium.