Question

A dynamic ram has refresh cycle of 32 times per msec. Each refresh operation requires 100 nsec and a memory cycle requires 250 nsec. What percentage of memorys total operating time is required for refreshes?

Answer 1

The percentage of memory's total operating time required for refresh is 0.32 %

Explanation :

Memory cycle time = 250nsec = 250 x 10⁻⁹ s

Number of refreshes in 1 msec = 32

=>Number of refreshes in 1 s = 32000

=> Number of refreshes in 250 x 10⁻⁹ s = 32000 x 250 x 10⁻⁹

= 8 x 10⁻³

Time taken by 1 refresh cycle = 100 nsec = 100 x 10⁻⁹ = 10⁻⁷ s

=> Time taken by 8 x 10⁻³ refresh cycles = 8 x 10⁻³ x 10⁻⁷

= 8 x 10⁻¹⁰ sec

Hence percentage of time for refresh = 8x10⁻¹⁰/250x10⁻⁹  x100%

= 0.32 %