Magnetic disk apparatus and method

A method of controlling a magnetic disk apparatus, the magnetic disk apparatus including a magnetic disk, a flash memory, and a volatile memory, the flash memory including memory cell transistors whose threshold voltages are set to a first section or a second section, the first section corresponding to a first value, the second section corresponding to a second value, the second section being on a lower voltage side than the first section, the volatile memory serving to hold first data being data received from a host device until the first data is written onto the magnetic disk, the method comprising:

• performing bit inversion of second data being the first data held in the volatile memory and writing the second data onto the flash memory when a power loss occurs in a case where the second data corresponds to third data, the third data being data in which a number of the first values is larger than a number of the second values;
• and
• writing the second data onto the flash memory without performing bit inversion when a power loss occurs in a case where the second data corresponds to fourth data, the fourth data being data in which a number of the first values is smaller than a number of the second values.