When a hard disk drive is being accessed, the __________ spins and the __________ moves until the head is over the proper location on the disk.

• A. Spindle, arm
• B. Platter, arm
• C. Head, arm
• D. Arm, head

Answer: (B)

Hard disk access relies on two coordinated motions: the storage surfaces must rotate so data can be read, and the read/write head must be positioned over the correct track. The platters (the disk surfaces) spin around a spindle motor, providing the continuous surface under the head. The read/write head is mounted at the end of the actuator arm, which pivots to move the head radially to the proper location on the disk. So when data is being accessed, the platter spins and the arm moves until the head is over the right track. The other options mixes up which component performs rotation versus positioning—the head doesn’t spin by itself, and the arm’s role is to position the head rather than spin.