Provided is a unit for protecting data with respect to data transfer between memories of a disk controller. The disk controller for controlling data transfer between a host computer and a disk drive includes: a channel unit having a channel memory; a cache unit having a cache memory, and a control unit for controlling the data transfer. The data transferred to/from the host computer is transferred in a packet between the channel memory and the cache memory, and The control unit for verifying consistency of information included in a header of the packet to be transferred to decide whether transfer can be permitted when the packet is transferred.