# What is rotational latency in the context of disk access time? – IGNOU MCA Assignment 2014 – 15

By | October 2, 2014

MASTER OF COMPUTER APPLICATIONS
Course Code : MCS-012
Course Title : Computer Organisation and Assembly Language Programming
Assignment Number : MCA (2)/012/Assign /2014-15
Maximum Marks : 100
Weightage : 25%

What is rotational latency in the context of disk access time? Assume that the disk rotates at 6000 rpm; each track of the disk has 16 sectors; data transfer rate of the disk is 64 MB/second; and average seek time of disk is10 millisecond. Calculate the average access time for the disk.

Disk Rotation Speed = 6000 rpm

Sectors per Track = 16 sectors

Data transfer rate = 64 MB/second

Average seek time = 10 millisecond

Convertion is Shown Below: Rotational latency = Average seek time + Average Rotational delay + Transfer time + Controller Overheads

Average seek time = 10 millisecond (given)

Calculate

Average Rotational delay = ½ Time of Rotation in milliseconds

Average Rotational delay = ½ * (60/6000) *1000 millisecond

= ½ * 10 millisecond

= 5 millisecond

Calculate

Transfer time = Block size / Transfer rate

Block size =? (Not Mentioned)

Assume = 1 KB per 1 sector

So 16 sector = 16 KB

Transfer time = (16 KB / 64 MB/sec)

= (16 / 64) millisecond

= 0.25 millisecond

Note:-  Controller Overheads (optional) not using it For Now.

Rotational latency = Average seek time + Average Rotational delay + Transfer time

Rotational latency = 10 millisecond + 5 millisecond + 0.25 millisecond

= 10 + 5 + 0.25 millisecond

= 15.25 millisecond.