What does a controller control?

a. the ports for removable storage devices

b. the interface between the hard disk and the system bus

c. the interface between the hard disk and the operating system

d. the electronic circuits that control the platters?

b. the interface between the hard disk and the system bus

Explanation:

A controller, in the most basic computing terms, is a hardware chip or card that falls between two hardware components. Thus, a computer's motherboard will always have a controller that interfaces with RAM, hard disk, DVD drives or other hardware components. Being an interface between two hardware devices facilitate incoming and outgoing commutations. Option B therefore, is the correct answer because it interfaces between the hard disk and sytem bus, which are both hardware components.