What do you understand by DRAM and its refreshing?
Dynamic RAM (DRAM) is fundamentally the same as SRAM, but this retains data for only 2 or 4 ms on an internal capacitor. But after 2 or 4 ms, the contents of the DRAM should be fully rewritten (refreshed) since the capacitors that is store logic 1 or logic 0, lose their charges. The whole content of the memory is refreshed with 256 reads in a 2-to-4 ms interval. Also refreshing occurs throughout a write, a read or a particular refresh cycle.