DOS, wasn't really multitasking OS anyways. I think my main point is, is it hard to preserve and give OS high priority over all other applications? If it is no

DOS, wasn't really multitasking OS anyways. I think my main point is, is it hard to preserve and give OS high priority over all other applications? If it is not hard, is a big downside for app developers if they don't get 100% control over the CPU cycles? Why is it necessary these days that apps have the ability to push 100% on multiple cores? At the least with multiple cores, shouldn't 1 core be dedicated to the OS, so it never hangs due to another app? Something sacred, with a lot of gates so devs cannot mess up the entire OS and user experience due to their app.