The difference between RAM (Random Access Memory) and ROM (Read-Only Memory) lies primarily in their functionality and purpose in a computer. RAM is a type of volatile memory used for temporarily storing data that the CPU needs during operation, allowing for quick read and write access. In contrast, ROM is non-volatile memory that permanently stores firmware and system software, which is critical for booting the computer. While RAM is fast but loses its data when power is off, ROM retains its information even without power, ensuring essential functions remain intact.