OPTICAL DISK DEVICE AND READ CACHE METHOD

PROBLEM TO BE SOLVED: To actualize an efficient read cache system which has small waste even when read commands which are successive in sequence are issued and even when a read command for a file, etc., is issued. SOLUTION: A data processor reads data corresponding to a specified preread amount out from a specified position on an optical disk and stores them in a read cache area of a RAM. A CPU reads the data out of the read cache area (S3) and provides them for a host device when data corresponding to the read range of the read command from the host matches the data stored in the read cache area. The CPU judges a transfer rate of reading that the host requests (S6) and compares the requested transfer rate with the rate of the data read from the optical disk by this device. According to the requested transfer rate of the host, the preread amount is set (S7, S8, S9).