Patent ID: 8504762

Claim:
A semiconductor storage device connectable to a host, the storage device comprising: a package; a controller disposed in said package and having an interface circuit configured to control data input and output between the host and the storage device so that the semiconductor storage device is operated as a drive compatible to a hard-disk-drive as viewed from the host; a first memory unit configured with flash memories disposed in said package and configured to provide a file management information section, which is configured to store file management information of an operating system for the host, and a data section configured to store data sent from the host in the data section, wherein the file management information is to be referred to when the host accesses the data section; a second memory unit configured with one of static and dynamic random access memories disposed in said package; and a power supply maintaining unit disposed in said package and including an electric capacitor having a capacity of at least 0.1 F, wherein, while the host is under a normal operation, the semiconductor storage device is driven by electric power supplied by the host, and the electric capacitor is charged by the electric power supplied by the host, and wherein the controller is configured to: (1) read file management information from the first memory unit configured with flash memories and write the same in the second memory unit configured with one of static and dynamic random access memories in response to startup of the host; (2) perform read and write operations from the host to the storage device by referring to the file management information stored in the second memory unit configured with the random access memories instead of the file management information in the first memory unit configured with flash memories, and update the file management information within the second memory unit configured with the random access memories during normal operations of the host when an access of read or write from the host to the storage device is observed; (3) read the updated file management information in the second memory unit configured with the random access memories and write the same in the first memory unit configured with flash memories in response to a normal shutdown operation in the host; and (4) when an unexpected power shutdown occurs on the host side, switch power supply connection from the host to the power supply maintaining unit and control to cut off a signal from the host and read the updated file management information in the second memory unit configured with the random access memories and write the updated file management information in the first memory unit configured with flash memories with electric power supplied from the power supply maintaining unit.