Refresh:

Consider a memory system that has a capacity of 256 GB, that is made up of 16 ranks, each rank having 8 banks. Assume that every refresh command triggers a parallel refresh in every bank in every rank. How many rows are refreshed in each bank on every refresh command? Assume it takes 50 ns on average to refresh each row in a bank. For what fraction of time is the memory system unavailable? Assume that a row in a bank has a capacity of 4 KB. Assume that every row must be refreshed within 64 ms and a refresh command is issued every 7.8 us.