A memory controller implements flexible memory mapping for storage of data units in a memory. The memory controller logically partitions the memory into a plurality of blocks or block segments and manages the storage of data units among the plurality of blocks/block segments. The memory controller can operate in one of three modes: a monolithic mode whereby the memory is modeled as a plurality of blocks, whereby each block is treated as a “monolithic” block; a fragmented mode whereby the memory is modeled as a plurality of blocks segments of varying sizes; and a combined mode whereby the memory is initially partitioned into a plurality of equal-sized blocks, and whereby each block can be used as a monolithic block or a fragmented block comprising a plurality of block segments of different sizes, and wherein monolithic blocks can be converted to fragmented blocks and fragmented blocks can be converted back to monolithic blocks.