sentences:  For example, a system with 213 = 8,192 rows would require a staggered refresh rate of one row every 7.8 µs which is 64 ms divided by 8,192 rows.A few real-time systems refresh a portion of memory at a time determined by an external timer function that governs the operation of the rest of a system, such as the vertical blanking interval that occurs every 10–20 ms in video equipment.The row address of the row that will be refreshed next is maintained by external logic or a counter within the DRAM.