Memory system

A memory system connectable to a host, the memory system comprising:

• a nonvolatile memory including a plurality of memory cells;
• and
• a controller configured to write data to the nonvolatile memory in either a first mode or a second mode, a number of bits of data written in a memory cell in the second mode being larger than a number of bits of data written in a memory cell in the first mode, wherein
• the controller is further configured to:
• write data, which is received from the host, into a first region of the nonvolatile memory in the first mode;
• upon an available unused capacity on the memory system being smaller than a threshold, change a mode to write data to the nonvolatile memory from the first mode to the second mode;
• and
• write the data stored in the first region into a second region of the nonvolatile memory in the second mode.

A control method of controlling a memory system that is connectable to a host and comprises a nonvolatile memory including a plurality of memory cells, the control method comprising:

• determining a size of a first region of the nonvolatile memory in the memory system based on an available unused capacity on the memory system;
• writing data, which is received from the host, into the first region in a first mode;
• and
• upon a size of an available area in the first region being smaller than a threshold, writing the data stored in the first region into a second region of the nonvolatile memory in a second mode, a number of bits of data written in a memory cell in the second mode being larger than a number of bits of data written in a memory cell in the first mode.

A control method of controlling a memory system that is connectable to a host and comprises a nonvolatile memory including a plurality of memory cells, the control method comprising:

• writing data, which is received from the host, into a first region of the nonvolatile memory in a first mode;
• upon an available unused capacity on the memory system being smaller than a threshold, changing a mode to write data to the nonvolatile memory from the first mode to a second mode, a number of bits of data written in a memory cell in the second mode being larger than a number of bits of data written in a memory cell in the first mode;
• and
• writing the data stored in the first region into a second region of the nonvolatile memory in the second mode.