Data being stored in a block of flash memory system may be characterized as being frequently modified or infrequently modified (hot/cold) based on a heuristic. When performing garbage collection, if the data from hot blocks is consolidated and data from cold blocks is separately consolidated by writing the data to different free blocks, the number of write operations to perform the garbage collection may be reduced. The lower “write amplification” contributes to increasing the lifetime of the memory circuit. When the number of blocks in a pool of previously erased blocks is reduced to a threshold value, a block having data previously stored therein may be selected for garbage collection based on a second heuristic.