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

  1. $0.64$
  2. $0.96$
  3. $2.00$
  4. $0.32$
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TIME REQUIRED TO REFRESH 32 IN I MS IS 32 x 100 ns =3200 ns
percentage of memory total operating time is required for refreshes = = 3200 ns/1000000 x 100% = 0.32%

Answer : D

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Ans: (4)  0.32
In 1 msec, refresh=32 times
memory cycle= 1msec/250nsec= 4000 times

Therefore % refresh time:
(32*100nsec)/(4000*250nsec) 
= 3200/1000000=0.0032 
= 0.32%


One can also refer:
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 % 

Refer:
https://brainly.in/question/7072365#readmore

edited by
2 votes
2 votes

First we will find how many no cycle will be there in one memory operation-
 

Given that in 1 msec(106 nsec) no of refresh cycle =32 cycle

then we can find cycle in 250 nsec (which is 1 memory cycle time) no of refresh cycle = (32*250)/106 cycle

Now we can find total time taken by refresh operation in 1 memory cycle

1 cycle of refresh operation required 100 nsec

(32*250)/106 cycle of refresh operation required = ((32*250)/106)*100= 0.8 nsec

now find percentage of memory's total operating time is required for refreshes (100/250)*0.8 = 0.32%

Answer:

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