Operating System

1:

A program P reads and processes 1000 consecutive records from a sequential file F stored on device D without using any file system facilities. Given the following:
(i) Size of each record = 3200 bytes.
(ii) Access time of D = 10 m secs.
(iii) Data transfer rate of D = 800 x 103 bytes/sec
(iv) CPU time to process each record = 3 m secs.

What is the elapsed time of P if F contains unblocked records and P does not use buffering?

A.

12 sec

B.

14 sec

C.

17sec

D.

21sec

 

Answer : C

Explanation :

In case P uses one 'Read ahead' buffer the processing and transferring of records can be overlapped.

 Elapsed time =(Access time+ Transfer time + Processing Time )x (Number of records)

Here Access time = 10ms (given)

Transfer time = (800 x 103 )/3200 sec = 0.004 sec = 4 ms

Therefore Elapsed Time =  (10 + 4 +3 ) * 1000 m sec = 17 sec.

Here processing time is less than transfer time.

Appasami said: (7:47pm on Saturday 2nd June 2018)
Transfer time = 3200 /(800 x 10^3 ) sec = 0.004 sec = 4 ms

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Option: A

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