Staggered stream support for video on demand

(57) A summary video-file server (20) contains two or more stream server computers (21) which really link ICDA to a data network (25) for transmission of a cache disk array storage subsystem (ICDA, 23) and a video-data stream. Further, a video-file server contains the server controller (28, 29) which specifies a stream server in order to serve a client request for a client request with the application of a permission control policy. A stream server supports at least one industrial standard network file access protocol and one file access including real time スケジュラー (63) for carrying out scheduling of the isochrony task (83) for continuation medium file access. The data which ICDA answered the video prefetch command and was specified to the prefetch command for a certain process, It is held at the quota portion of cache memory until ICDA answers the fetch command which specifies data for the process, since ICDA answered the prefetch command. The time between pre fetching is chosen based on the disk (47) and cash (41) resource which can be used. A video-file server offers video-on-demand service by maintaining the sliding window of the video data of the random access memory (91, 92, 93, 94) of a stream server computer, and assigning dynamically.