Re: Multi-Tasking on Apple IIgs?

[et472@FreeNet.Carleton.CA (Michael Black)]

"Bryan Parkoff" (nospam@nospam.com) writes:
>     Is there a way to write assembly language that can run two applications 
> at same time as multi-tasking?  It has to run first application and then 
> switch to run second application at the same time.  It may be the Program 
> Counter register that it can be modified.  I don't know how like Intel did.
> 
> Bryan Parkoff
> 
> 

Any microprocessor can multi-task.  Of course, if you have limited memory
it can be troublesome, since you either can't do much, or you have to
move stuff in and out of memory.  You generate an interrupt, which causes
the CPU to deal with it, saving the register values and then doing the
something else.  Do it fast enough, and it looks like everything is
working at the same time.

Microware had a multi-tasking monitor rom for the 6800, before going
on to create OS-9 for the 6809.  That was an 8-bit CPU, albeit better
than the 6502 or 6800.

Multi-tasking is not really a complicated thing, though much of the time
when it's added we are seeing a much fancier operating system which makes
it seem like multi-tasking is complicated.

The real issue in making an existing computer multi-tasking is that you
can't start with a clean slate.  It may be problematic to impose it
on an existing operating system or ROM monitor, and making sure that
it doesn't affect any application running on top.  If you are writing
from scratch, you write everything so it doens't do weird things (like
self-modifying code).

  Micahel