GATE | GATE CS 2010 | Question 65

A main memory unit with a capacity of 4 megabytes is built using 1M × 1-bit DRAM chips. Each DRAM chip has 1K rows of cells with 1K cells in each row. The time taken for a single refresh operation is 100 nanoseconds. The time required to perform one refresh operation on all the cells in the memory unit is:- 
A.100 nanoseconds
B.100×2¹⁰ nanoseconds
C.100×2²⁰ nanoseconds
D.3200×2²⁰ nanoseconds

(A)

(B)

(C)

(D)