We can also introduce associative systems as a special case of the synchronous class . This class includes content-addressable memories and associative processors, but we will not discuss this topic further in this book. This corresponds to a general distributed-memory MIMD machine with each node typically executing distinct programs and with varying and unsynchronized internode message traffic. They have generally disparate members evolving with possibly different temporal algorithms. The majority of large scale scientific and engineering computations are synchronous or loosely synchronous as exemplified by the contents of this book.
Society shows many examples of loosely synchronous behavior.
Vehicles proceed more or less independently on a city street between loose synchronization points defined by traffic lights. The reader's life is loosely synchronized by such events as meals and bedtime. When we consider computer hardware and software systems, we will need to consider other temporal classes which can be thought of as further subdivisions of the asynchronous class. This translates into a MIMD software model of static processes interacting with a general dynamic message-passing system. We have a fixed number of processes which are spawned and then execute a particular program which remains unchanged.