multitasking

[psxphill]

To me the Amiga was the first true multitasking computer. Preemptive multitasking is what it uses from memory.
 
http://en.wikipedia.org/wiki/Preemption_%28computing%29

First pre-emptive multitasking desktop computer, even Windows and MacOS didn't have it. However many mainframe and workstations did.