Yes, delete them manually.
A computer without an operating system will not operate.
Practically all of them have O.S's, as I doubt that most people will ever see one without some mac o.s on it or xp or vista on it. However, all stock machines that are loaded/downloaded/installed with programs/software,etc come without operating systems. I have seen my share of them, as I used to work for a computer store myself, though DOS is nothing to brag about, unless you are some nerdy IBM veteran that designed it.
A Mac computer is a personal computer. The term PC has become synonymous with personal computers running the Windows operating system but any stand alone computer can be described as a personal computer.
If you have an image for you OS system partition you can recover it, if you have an advance OS you can refresh it without formatting like "win 8 or 10", you can do a system repair for your OS without affect or loose you files but not recommended, otherwise you have to make new operating system.
The operating system is the most important part of a operating system because without an OS you will not be able to do anything with your computer and it will effectively be useless, instead of a computer you have a pile of components that does nothing
fill without formatting
Because without an operating system, your computer will not be capable of doing anything useful.
No, but it won't function without one.
No. You need an operating system to do the installing.
Personal computer
The operating system (OS) supplies the user interface by which there is an interaction. No OS = expensive paperweight (can't use the hardware)
A computer can not operate without an os, different OS's have different UI,s