(SOLVED) Caculation

Assume a disk rotates at 5,000 RPM with an average rotation of 0.5 round. The average seek time is 5 ms. The data transfer rate is 200MB/sec. There is a controller overhead of 0.1 ms. What is the estimated average latency to read or write a 512B sector?

Expert Answer

Disk latency to read and write = Seek Time + Avg. Rotation Time + Transfer Time + Controller Overhead

Average Rotational Time = (0.5*60)/(5000) = 6 ms
[On average half rotation is made]

Avg. Seek Time = 5 ms

Transfer Time = 512 / (200 × 106 B/s)
              = 2.56 microsec

Controller Overhead = 0.1 ms

Disk latency = Seek Time + Rotation Time + Transfer Time + Controller Overhead
             = 5 + 6 + 2.56 * 10-3 + 0.1 milliseconds
             = 11.10256 milliseconds