It is not true that a computer needs ROM and RAM to work.
Information to include in the answer: Computers do not need an operating system or any program in order to function.
Computer storage devices such as hard drives and flash memory can store programs and data. They provide much larger amounts of storage than the little amount of integrated CPU cache typically found inside a CPU chip, which typically stores around a few dozen kilobytes – dozens of megabytes at most. Typically, CPUs are more powerful for certain types of calculations, while non-volatile memories are more suited for other types of tasks.