Semiconductor storage device with volatile and nonvolatile memories to allocate blocks to a memory and release allocated blocks

A method of controlling a storage device, the storage device including a nonvolatile memory including a plurality of blocks, each of the plurality of blocks being a unit of data erasing and configured to store a first data of a first bit, the method comprising:

• allocating a first set of the plurality of blocks as a first memory area, the first set of the plurality of blocks each including a first block having a memory cell configured to store a second data of a second bit, the second bit being less than the first bit;
• allocating a second set of the plurality of blocks as a second memory area, the second set of the plurality of blocks each including a second block having a memory cell configured to store the first data;
• receiving data from an external host apparatus;
• storing the received data into the first block in the first set of the plurality of blocks by a first management unit, the first management unit being less than the unit of data erasing;
• copying valid data stored in the first block to the second block by a second management unit, the second management unit being corresponding to the unit of data erasing and being larger than the first management unit;
• and
• releasing the first block in which no valid data is stored, after copying the valid data stored in the first blocks,
• wherein the first block includes a pseudo block configured to be capable of storing the first data but storing the second data.