Certainly if you do not call out to DOS or the BIOS! All the time with DOS we would write text to the screen by writing it into memory because it was so fast and if you wrote a terminal emulator you would catch the interrupts and write to the UART registers in assembly or C or Turbo Pascal. You only needed DOS for the filesystem otherwise the application could do anything that DOS could do.

Old versions of Linux had a giant lock on the whole kernel which would let only one CPU enter the kernel at once. You could probability protect DOS the same way at the cost of scalability.