Why is defragmentation useful on a traditional hard disk but generally unnecessary on a solid state drive?

Correct answer: A solid state drive does not require a mechanical head to move for data access

The governing concept is the difference between magnetic storage and flash storage. A traditional hard disk uses a moving read/write head, so scattered file fragments can increase seek time; defragmentation places them more contiguously. An SSD uses electronic flash memory and has no mechanical head, so fragmentation does not create the same access delay. Therefore D is correct, while A, B, and C are false.