Patent ID: 8782331

Claim:
A solid state drive comprising: an interface controller configured to receive data provided from an external host apparatus; a first memory configured to write the data by a first unit or less, the first unit being an access unit from the external host apparatus; a nonvolatile memory configured to store data transmitted from the interface controller via the first memory in at least one of a plurality of blocks and write transmitted data by a second unit, each one of the plurality of blocks being a unit of data erasing, and the unit of data erasing being twice or greater natural number times as large as the second unit; and a drive controller coupled with the interface controller, the first memory and the nonvolatile memory via at least one internal bus, the drive controller is configured to: allocate a plurality of blocks to a first memory area, the plurality of blocks allocated to the first memory area including SLC (Single Level Cell) blocks; allocate at least one of the SLC blocks to a second memory area, a plurality of blocks allocated to the second memory area including SLC blocks and MLC (Multi Level Cell) blocks; store a plurality of data by the first unit in the first memory; store a data from the first memory in the SLC block in the first memory area by a first management unit, the first management unit being twice or larger natural number times as large as the first unit and being less than the unit of data erasing; release a block in which all the data of the first management unit become invalid data among the plurality of blocks allocated to the first memory area; copy valid data stored in the SLC blocks to one of the MLC blocks, within the second memory area, when a predetermined condition is satisfied; and release at least one of the SLC blocks in which no valid data is stored from the second memory area, after copying the valid data stored in the SLC blocks.