Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!zaphod.mps.ohio-state.edu!uakari.primate.wisc.edu!dogie.macc.wisc.edu!uwvax!astroatc!nicmad!madnix!jason
From: jason@madnix.UUCP (Jason Blochowiak)
Newsgroups: comp.sys.apple
Subject: Harvard Architecture (was Re: Apple single and ......)
Message-ID: <1179@madnix.UUCP>
Date: 16 Mar 90 11:18:18 GMT
References: <3602.25f919c8@vax5.cit.cornell.edu>
Reply-To: jason@madnix.UUCP (Jason Blochowiak)
Distribution: comp
Organization: ARP Software, Madison, WI
Lines: 34

q4kx@vax5.cit.cornell.edu (Joel Sumner) writes:
>1.  Could someone please explain exactly what "Harvard Architecture" is and
>how it affects the 65816 (or how it is implemented in a processor)?

	A Princeton architecture (also known as a Von Neumann machine)
consists of (basically) a CPU and some memory. That memory can function as
either data or code.

	The Harvard architecture, on the other hand, has a CPU, code memory,
and data memory. The one major problem with this is that code is sometimes
data, and so it didn't get real popular for a long time. Well, people are
getting interested in it again, now that it's possible to have multiple
segments - it makes caching code easier, as the CPU won't have to re-fetch
the code from main memory ever (assuming there's enough space in the
cache), as it won't change.

	Now, the 680x0's architecture discourages self-modifying code, so
it's not too painful for it to go Harvard, but the 65816 & 6502 programmers
of the world do use self-modifying code (despite the fact that it's a real
pain to debug), and that would pretty much invalidate the entire code/data
separation.

	Good enough?

> [#2 was something else...]
>Thanks
>Joel
>q4kx@cornella


-- 
                      Jason Blochowiak - jason@madnix.UUCP
or, try:         astroatc!nicmad!madnix!jason@spool.cs.wisc.edu
       "Education, like neurosis, begins at home." - Milton R. Saperstein