Win3.1 supports co-operative multi-tasking. Once a process
is given the control for execution, the other tasks have to
wait until the current has relinquished its execution.

WinNT is preemptive multi-tasking. A process can be stopped
in the middle if another process needs CPU cycle.
This is handled by the windows OS.

Win 3.1 supports process based multi tasking. If one process
run, it wont allow another process until that process
completed. This will command the CPU cycles. This is non-
preemptive multitasking.