The Multitasking Executive, better known as Exec, is the heart of the
Amiga's operating system.  All other systems in the Amiga rely on it to
control multitasking, to manage the message-based interprocess
communications system, and to arbitrate access to system resources.
Because just about every software entity on the Amiga (including
application programs) needs to use Exec in some way, every Amiga
programmer has to have a basic understanding of its fundamentals.

 multitasking                 interprocess communications 
 dynamic memory allocation    libraries and devices 
 signals