A heterogeneous memory system includes a main memory arrangement, a first-level cache, and a memory management unit (MMU). The first-level cache includes an SRAM arrangement and a DRAM arrangement. The MMU is configured and arranged to read first data from the main memory arrangement in response to a stored first value associated with the first data and indicative of a start time. The MMU selects one of the SRAM arrangement or the DRAM arrangement for storage of the first data and stores the first data in the selected one of the SRAM arrangement or DRAM arrangement. The MMU reads second data from one of the SRAM arrangement or DRAM arrangement and writes the data to the main memory arrangement in response to a stored second value associated with the second data and indicative of a duration.