File and Input/Output System Q.25

25A 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?

Option : 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.

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