[G4] dual processors

[Jonathan Armstrong]

On Sep 8, 2005, at 8:50 PM, Perry The Cynic wrote:

> --On September 8, 2005 9:27:15 PM -0500 Bob Schmidt  
> <bob58523 at charter.net> wrote:
>
> Macintoshes running Mac OS X use "symmetric multiprocessing." Both  
> processors have "equal rights;" there is no "master" and "standby"  
> processor.
>
> Of course, if your Mac doesn't do much right now, the system will  
> slow down one processor to save energy (and heat). And if you only  
> run one program and that program isn't multi-threaded (written to  
> use multiple processors), then you will see one processor work for  
> that program and the other taking care of the rest of the system  
> (background activity, graphics, etc.)
>
> Note that all this was *not* true in Mac OS 9, where the second  
> processor can only be used for a very limited set of activities.

Not strictly true; OS 9 has a true SMP micro kernel, so it can run on  
either processor, or switch between the two on a context switch. It  
just happens to be the case that most of OS 9, including the  
applications it launches, runs in a single thread. Any process can  
also create additional peer threads, but the other threads are not  
permitted to make some important OS calls (mainly GUI).