Patent ID: 7154805

Claim:
A storage device employing a flash memory, wherein said flash memory is divided into a plurality of physical sectors identified by physical addresses, wherein said flash memory carries out data write operation of write data from a host system into a sector of said plurality of physical sectors in response to a host logical address accompanied with said write data from said host system, said storage device includes: a memory controller which generates a physical address in response to said host logical address for said data write operation of said write data from said host system, wherein said memory controller carries out address conversion from host logical addresses to physical addresses, wherein said memory controller carries out a current data write operation in which current write data from said host system is written into a selected one sector of said plurality of physical sectors identified by a current physical address which is converted by said memory controller from a current host logical address, and said memory controller carries out a succeeding data write operation in which succeeding write data from said host system is written into a selected another one sector of said plurality of physical sectors identified by a succeeding physical address which is converted by said memory controller from the succeeding host logical address that is identical to said current host logical address, and wherein said succeeding data write operation is carried out within said storage device even though said selected one sector of said plurality of physical sectors is not defective and is usable before said succeeding data write operation so that said memory controller carries out lowering of differences of frequencies in usages of data writing operations among said plurality of physical sectors due to differences of frequencies in usages data writing operations among a plurality of host logical addresses, wherein said memory controller seeks an old physical sector of said specific host logical address in which unnecessary data is written and carries out an erase operation of unnecessary data in said old physical sector among said plurality of physical sectors, wherein said memory controller stores a new correspondence between a new physical sector to the specific host logical address within a table for said address conversion, said new physical sector is identified by a new physical address converted from said same identical specific host logical address by said memory controller, wherein said memory controller is provided with a volatile memory to store data, and wherein said data of said volatile memory is originated from data stored in said flash memory by said memory controller at the start of operation of said storage device, and then said memory controller controls the operation of said non-volatile semiconductor flash memory based upon said data stored by said volatile memory.