Both are subject to wear and tear and environmental hazards and have therefor only limited lifetime. Both serve to forward some desired information to the program presently running on the computer. With the keyboard we do this by pressing either a single key or a combination of keys. After turning the power on, the CPU gets its instructions first from the ROM where they had been permanently implanted by the computer's manufacturer. Because many instructions are needed over and over again it saves a lot of time to copy the set of instructions making up the OS only once from the disk to memory and leave them there for future use.
Operating systems come in a variety of different flavors.
Most personal computers which are called IBM compatible are running under DOS, various Microsoft Windows products 3.1 or NT or 95 or 98. In reality things are a little bit more complicated because you want to store larger integer numbers, negative integer numbers, and decimal numbers as well. Furthermore, letters of the alphabet and other symbols are stored as numbers. Early in the computer age people had agreed which letter is associated with which number. Your editor is configured such that when it reads a particular number from the data file it knows which letter corresponds to that number and puts the letter onto the screen for you.