A computer system includes a processor coupled to a DRAM through a memory controller. The processor switches the DRAM to a low power refresh mode in which DRAM cells are refreshed at a sufficiently low rate that data retention errors may occur. Prior to switching the DRAM to the low power refresh mode, the processor identifies a region of an array of DRAM cells that contains essential data that needs to be protected from such data retention errors. The processor then reads data from the identified region, and either the DRAM or the memory controller generates error checking and correcting syndromes from the read data. The syndromes are stored in the DRAM, and the low power refresh mode is then entered. Upon exiting the low power refresh mode, the processor again reads the data from the identified region, and the read data is checked and corrected using the syndromes.