What is the most common speed in rpm at which the hard disk usually rotates ........

Explanation:

Ans: B . 3600

The most common speed in rpm at which the hard disk usually rotates is 3600.

For the RPM specification, platters need to spin faster to increase performance in a hard drive. This results in moving the data bits past the read/write head faster, which results in higher data rates. Hard drives have been engineered with spin rates as low as 1,200 RPM and as high as 15K RPM. But today’s most common RPM rates, in both laptop and desktop PCs, are between 5,400 and 7,200 RPM. But the most common is 3600 rpm.