Harvard vs. vonNeuman - test-drb@ccmp.vtda.org

28 Sep 2004

...
 Part of the issue, for modern machines, is that the
hardware gets in
the way.  If you change code, the I-cache doesn't change (in machines
I'm familiar with) so the old instruction may still execute.  This
makes instruction modification a tricky business.  Debuggers do it,
operating systems do it -- and both have to pay attention to all the
cache magic you have to perform for it to be right. 
This reminds me of a point I wanted to make earlier and forgot - another
big issue us that SOFTWARE gets in the way! - todays computing world is
much more oriented toward sharing code, and many systems support multiple
execution threads of a single copy in core - it causes bad things to
happen when one of those threads changes the code :-)

Regards,
Dave
-- 
dave04a (at)    Dave Dunfield
dunfield (dot)  Firmware development services & tools: www.dunfield.com
com             Vintage computing equipment collector.
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