From mboxrd@z Thu Jan  1 00:00:00 1970
From: mike.ab3ap@gmail.com (Mike Markowski)
Date: Sun, 13 May 2018 17:44:27 -0400
Subject: [TUHS] The birth of the Z3
In-Reply-To: <20180513213042.0914C18C09C@mercury.lcs.mit.edu>
References: <20180513213042.0914C18C09C@mercury.lcs.mit.edu>
Message-ID: <86258450-6c66-1a5e-c18c-392f0fd4ec8f@gmail.com>

On 05/13/2018 05:30 PM, Noel Chiappa wrote:
>      > From: Clem Cole
> 
>      > Their is a open question about the need to support self modifying code
>      > too. I personally don't think of that as important as the need for
>      > conditional instructions which I do think need to be there before you
>      > can really call it a computer.
> 
> Here's one way to look at it: with conditional branching, one can always
> write a program to _emulate_ a machine with self-modifying code (if that's
> what floats your boat, computing-wise) - because that's exactly what older,
> simple microcoded machines (which don't, of course, have self-modifying code
> - their programs are in ROM) do.
> 
> 	Noel

Rewording that, as I recall from Computability Theory there are three 
statements needed for Turing completeness:

   1. S <- 0         S is some var
   2. S <- S + 1
   3. if S=0 goto L  L is some line#

Beyond that everything else is icing on the cake.  Kind of like needing 
nothing more than a bunch of NAND gates to build a computer, 
disregarding practicality...

Mike Markowski