GATE | GATE-IT-2004 | Question 51

The storage area of a disk has innermost diameter of 10 cm and outermost diameter of 20 cm. The maximum storage density of the disk is 1400bits/cm. The disk rotates at a speed of 4200 RPM. The main memory of a computer has 64-bit word length and 1µs cycle time. If cycle stealing is used for data transfer from the disk, the percentage of memory cycles stolen for transferring one word is

(A) 0.5%
(B) 1%
(C) 5%
(D) 10%


Answer: (C)

Explanation:
Inner most diameter = 10 cm
Storage density = 1400 bits/cm

Capacity of each track :
= 3.14 * diameter * density
= 3.14 * 10 * 1400
= 43960 bits

Rotational latency = 60/4200 =1/70 seconds

It is given that the main memory of a computer has 64-bit word length and 1µs cycle time.

Data transferred in 1 sec = 64 * 10⁶ bits
Data read by disk in 1 sec = 43960 * 70 = 3.08 * 10⁶ bits

Total memory cycle = (3.08 * 10⁶) / (64 * 10⁶) = 5%


Thus, option (C) is correct.


Please comment below if you find anything wrong in the above post.

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