Controller and memory system having the controller

A memory system includes: a memory device including first memory blocks, within which a single bit is to be programmed into a memory cell by using a single level cell (SLC) method, and second memory blocks, within which two or more bits are to be programmed into a memory cell by using a multi-level cell (MLC)-or-more method, and a controller configured to program first data in the first memory blocks by using the SLC method and then migrate the first data from the first memory blocks into the second memory blocks by using the MLC-or-more method, wherein the controller is further configured to read the first or second memory blocks according to a number of free blocks included in the first memory blocks, when the read request for the second memory block is received after the specific amount of time.