28 Sep
2004
28 Sep
'04
12:35 a.m.
On Mon, Sep 27, 2004 at 03:57:20PM -0700, Peter C. Wallace wrote:
On Mon, 27 Sep 2004, Tom Jennings wrote:
Self modifying code is _very_ strongly frowned upon when working with
halfway modern machines, because it messes up the I-caches (which
operate best when the memory theuy cache is read-only and there almost
guaranteed not to change under them) and therefore _hurts_ performance.
Regards,
Alex.
--
"Opportunity is missed by most people because it is dressed in overalls and
looks like work." -- Thomas A. Edison
re: Zuse, and stored-program, etc...
Actually many modern CPU's with caches are Harvard Architecture, the
instruction streams and data streams only being mixed on the memory of the
caches.
I've also heard that machines that mix data and instruction streams are more
properly called "Princeton achitecture"...
Isn't self modifying code pretty much deprecated these days (aside from
trampolines and such) On Sun, 2004-09-26 at 01:37, Hans B PUFAL wrote:
This web page also seems apropro :
http://irb.cs.tu-berlin.de/~zuse/Konrad_Zuse/Neumann_vs_Zuse.html
First, I don't mean to disparage Zuse's accomplishments, especially
under the circumstances he lived in, it's pretty amazing.
The idea-of-the-century wasn't machines that calculate automatically,
but machines-that-modify-themselves-as-part-of-normal-operation. Other
than particular logical arrangement, I don't see how the Zuse machines
are an architectural improvement over the IBM and Harvard relay
calculators.
In many ways it's an unfair comparison, the IBM machines had a nearly
unlimited budget, and poor Konrad sat by himself in his living room
punching programs into used 35mm film stock, never mind the war going on
around him.
Less well-known but historically more interesting is his 'planKalculus',
his algorithmic nomenclature he worked up to describe computer
programs. He even had chess-playing code! It's described in fair detail
in A HIST. OF COMP. 20TH CENT. (1980, MIT press) by Knuth.
(For the record, PICs are "Harvard architecture"; data and program
memory are separate. "von Neumann architecture" is program and data
stored in the same memory.)