US Patent 7966450 Non-volatile hard disk drive cache system and method

A non-volatile hard disk drive cache system is coupled between a processor and a hard disk drive. The cache system includes a control circuit, a non-volatile memory and a volatile memory. The control circuit causes a subset of the data stored in the hard disk drive to be written to the non-volatile memory. In response to a request to read data from the hard disk drive, the control circuit first determines if the requested read data are stored in the non-volatile memory. If so, the requested read data are provided from the non-volatile memory. Otherwise, the requested read data are provided from the hard disk drive. The volatile memory is used as a write buffer and to store disk access statistics, such as the disk drive locations that are most frequently read, which are used by the control circuit to determine which data to store in the non-volatile memory.