Everyone knows that if you buy a computer you should install an operating system. 20 years ago, it was DOS, today it is windows. My questions are : how the computer knows how to install them if it has no compiler yet (a computer knows only mashine language, zero and one)? is there a compiler in these programs? and if so, how do i do the same to my programs i have written in c language? how do i write a program in c language that would be on CD, and when i insert the CD into the computer without an operating system it will prints "hello world"? in what language did they write these operating system?