What is the average time to read or write a 512byte sector f

What is the average time to read or write a 512-byte sector for a typical disk rotating at 7200 RPM? The advertised average seek time is 8ms, the transfer rate is 20MB/sec, and the controller overhead is 2ms. Assume that the disk is idle so that there is no waiting time.

Solution

512 byte sector

rotating speed at 7200RPM

seek time =8ms

Disk Access Time = seek time + rotational delay + transfer time + controller overhead = 8 + (0.5*60*1000/7200) + (512/20*220)*1000 + 2   = 14.17 ms

the disk is idle so that there is no waiting time