Answer
There are two basic types of multitasking: preemptive and cooperative.
In preemptive multitasking, the operating system parcels out CPU time slices to each program. In cooperative multitasking, each program can control the CPU for as long as it needs it. If a program is not using the CPU, however, it can allow another program to use it temporarily. Windows NT, UNIX, Windows 95, the Amiga operating system and OS/2, use preemptive multitasking, whereas Microsoft Windows 3.x and the MultiFinder (for Macintosh computers) use cooperative multitasking.
Keywords:performance thread multi pre-emptive