External storage device and memory access control method thereof

A storage device, comprising:

• a non-volatile semiconductor memory which is electrically erasable;
• a system interface coupled with an external host system;
• and
• a controller reading data from said non-volatile semiconductor memory and transmitting said data to said host system via said system interface in response to a read command received by said system interface from said host system;
• and
• wherein said controller carries out data processing for sector data that has been read from said non-volatile semiconductor memory, and
• wherein said controller starts reading (N+n)th sector data from said non-volatile semiconductor memory for said data processing for said (N+n)th sector data, while said controller transmits Nth sector data that has been carried out said data processing, to said host system via said system interface, in response to said read command for successive sector data.