They are both hardware.
It is common for people to use the term “ROM” because it sounds more specialized than saying “memory,” but in fact, all data storage devices are energy lossless memories.
The ROM chips on your computer store very specific information called “boot loader.” As long as you know what kind of operating system you want to use at the time you turn it on, then no additional input or keystrokes are needed to get that operating system up and running. The boot loader is preprogrammed into the ROM chip so when power is applied to the machine its encoded instructions automatically load up and run before any application programs have a chance to start running themselves.