Memory system comprising blocks operable in parallel

A method of controlling a memory system including a nonvolatile semiconductor memory including a plurality of blocks as a unit of data erasing and a controller that selects, in writing data in the nonvolatile semiconductor memory, a required number of free blocks not including valid data from the nonvolatile semiconductor memory and writes data in the selected free blocks, the method comprising:

• classifying free blocks included in the nonvolatile semiconductor memory into a plurality of free block management lists using a set unit of blocks operable in parallel;
• acquiring, in acquiring a first free block at normal priority, the first free block from a free block management list in which a number of free blocks is larger than a first threshold;
• and
• acquiring, in acquiring a second free block at high priority, the second free block from the free block management list in which a number of free blocks is larger than the first threshold and a free block management list in which a number of free blocks is not larger than the first threshold.

An information processing apparatus comprising:

• a central processing unit;
• a main storage memory;
• and
• an external storage device, wherein
• the external storage device includes:
• a nonvolatile semiconductor memory including a plurality of blocks as a unit of data erasing;
• and
• a controller including a block selecting unit that selects, in writing data in the nonvolatile semiconductor memory, a required number of free blocks not including valid data from the nonvolatile semiconductor memory and a writing control unit that writes data in the selected free blocks, and
• the block selecting unit includes:
• a list unit in which free blocks included in the nonvolatile semiconductor memory are classified into a plurality of free block management lists using a set unit of blocks operable in parallel;
• a first free-block selecting unit that operates to acquire, in acquiring a first free block at normal priority, the first free block from a free block management list in which a number of free blocks is larger than a first threshold;
• and
• a second free-block selecting unit that operates to acquire, in acquiring a second free block at high priority, the second free block from the free block management list in which a number of free blocks is larger than the first threshold and a free block management list in which a number of free blocks is not larger than the first threshold.