OPERATION OF CACHE MEMORY

PURPOSE:To eliminate structural overhead and to transfer data to a host computer at high speed by counting the number of times for accessing data which is slightly larger than a reference value and registering it in a cache memory when access is executed for more than the previously decided number of times. CONSTITUTION:A read command for reading data on a disk 2 is transmitted from the host computer 7, a microcomputer 6 executes a command processing for deciding the transfer start sector and the length of data to be read. The number of the decided sectors is compared with the reference value for judging whether data that is read from the disk 2 is unconditionally stored in the cache memory 5 or not, size with eight sectors, for example. When it is less than eight sectors, data is possibly stored in the cache memory 5. Thus, a cache memory collation processing is executed. When data does not exist in the cache memory 5, data is read from the disk 2 and it is fetched into the cache memory 5.