Memory system using flash memory and method of controlling the memory system

A method of controlling a memory system using a flash memory where a logical block as a unit accessed by a computer is allocated to a physical block of the flash memory, comprising the steps of:

• predicting whether a write count of each logical block in the future is larger or smaller on the basis of the situation of access to that logical block;
• managing an erasure count of each physical block when that physical block is erased;
• and
• allocating a logical block having a write count which is predicted to be larger to a physical block having a smaller erasure count and allocating a logical block having a write count which is predicted to be smaller to a physical block having a larger erasure count.

A memory system using a flash memory where logical blocks each as a unit accessed by a computer are allocated by allocation means to physical blocks of the flash memory, comprising:

• a flash memory having a plurality of individually erasable physical blocks;
• table means for holding the relationship in correspondence between the logical blocks allocated by the allocation means and the physical blocks;
• first counting and managing means for counting and managing write counts of the respective logical blocks;
• first classifying means for classifying the logical blocks into a plurality of groups on the basis of the respective write counts of the logical blocks;
• erasure means for erasing data in a physical block allocated to a logical block to produce a free physical block;
• second counting and managing means for counting and managing the erasure counts of the respective physical blocks;
• second classifying means for classifying the physical blocks into a plurality of groups on the basis of the respective erasure counts of the physical blocks;
• control means for allocating the respective logical blocks to the physical blocks;
• and
• means for managing free physical blocks which are not allocated to any logical blocks;
• wherein said allocation control means performs an exchanging process as required which comprises the steps of allocating a logical block belonging to a logical block group having a larger write count to a free physical block belonging to a physical block group having a smaller erasure count and allocating a logical block belonging to a logical block group having a smaller write count to a free physical block belonging to a logical block group having a larger erasure count.