Question

The seek time of a disk is 30 msec. it rotates at the rate of 30 rotations per second. each track has a capacity of 300 words. the access time is (a) 47 msec (c) 60 msec (b) 50 msec (d) 62 msec

Answer 1

It will be 62 or 60 msecs

Answer 2

Access time of hard disk is defined as time to access one word from hard disk memory  

It is given that, 30 rotations per second.

That is 1 rotation = 1/30 sec  

In 1 rotation, we can access 300 words (Capacity of each track)

For 1 word, we need 1/300 rotations  

So, 1 word transfer time = 1/300*1/30 sec  

Rotational delay = Average taken to be the time to rotate by half = 1/2 x time for 1 rotation = 1/2 X 1/30 seconds = 1/60 s = 16.6667 ms

So, avg access time= 30 ms(seek time)+ 1/60 sec (Rotational Delay)+ 1/9000 sec (transfer time)  

= 30 ms + 16.6667 ms + 0.1111 ms  

= 46.78 ms (approx)

So nearest answer is A. (47 m sec)