ROM is needed by the computer to store data so that it can be accessed when needed.
ROM is persistent memory, which means that even after power has been turned off, the memory module still retains its contents. This differs from system memory (RAM) which is only stored as long as there’s power on. Data stored on ROM needs to be loaded into RAM in advance before it can be acted upon or executed. It’s therefore usually used for simple instructions and programs like an operating system where space is limited and efficiency counts; more complex pieces of software are typically stored in larger pieces of (volatile) system memory instead since bigger blocks tend to access data faster than smaller ones – at least within one cycle of the processor clock.