Microsoft Windows prior to Windows’95 had what was called ‘cooperative multi-tasking’. This meant that a program had full-time access to the CPU until it (the program) released control to the operating system. The screen did not update and the mouse and keyboard did not respond if a program went off on a lengthy calculation or an unintentional infinite loop.
It was a necessary approach in the days of the 8086 and 80286 processors. Many complained about unresponsive systems and blamed the OS. In fact, with well written software, poor responsiveness was rare.
I like the approach. I accept the responsibility for not locking the UI when it gives me freedom from many of the issues in preemptive multi-tasking. Of course it helps that we have much faster computers and a good preemptive kernel to handle I/O.