Because without an operating system, your computer will not be capable of doing anything useful.
Use system restore, failing that reinstall M.E.
No. I believe TI83+ and TI84 do use an operating system.
It uses an android operating system.
It uses an android operating system.
It is a nintendo operating system
No, you cannot use Windows operating system on Mac Pro. Mac Pros are designed to work with macOS and you can't install a different operating system on them If you want to use a Windows operating system, you should go to the Microprokey website which is designed to work with Windows.
In general it doesn't matter what Network Operating System you choose, since they are integrated in the overall Operating System, and most use TCP/IP as the transport/routing model.
virtualization
There is no uninstaller for an operating system. To remove an OS, simply format the partition that holds the operating system. If you use a boot manager to choose between different operating systems the software should automatically detect missing operating systems for you.
the first computer to use operating system was mark1
It has its own firmware, it doesn't use an 'operating system' as such.
it should come into the system by default. if you are having trouble trying to use it then you could go to the help program of the operating system it should help you there.