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Re: The difference between programmable and non-programmable logic--if there is one.

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On 10/22/2011 6:14 PM, Robert Myers wrote:
> A recent Real World Technology article makes a big deal about the
> difference between programmable and non-programmable logic in talking
> about Intel's latest GPU's.
>
> So far as I know, every electronic circuit derives its usefulness from
> its ability to behave differently depending on state that comes from
> somewhere else. What's the difference between that and "programmable?"

I would beg to differ with that.  Electronic circuits are useful because 
they behave predictably, given known inputs.  A nand gate calculates a 
boolean result based on its inputs.  A latch stores the state of its 
input at some instant in time as defined by a clock.  The behavior of 
the logic is deterministic.
>
> The Von Neumann-Turing computing model is fairly rigid. It imagines an
> instruction stream driving the processing of a data stream. This model
> is already broken in numerous ways: interrupts, microcode, network
> inputs, peripheral cards, and all kinds of stuff outside the instruction
> stream that describe how a computer actually behaves.

In one model of computing, instructions and data are stored in the same 
space and are distinguishable only by context.  This arrangement makes 
the instructions vulnerable since there is no a-priori difference 
between the instructions and the data, and in fact in some cases the two 
are deliberately intermixed, as in self modifying code.
>
> Hacking exploits the fact that "instructions" don't have to come labeled
> as such and that nominally fixed-function logic can be made to do all
> kinds of strange things if you punch the right buttons in the right order.

Hacking in one form takes advantage of the fact that sometimes the 
behavior of a complex mechanism is not completely specified in the 
presence of unanticipated inputs.  The logic does not change its 
function.  Other times hacking takes advantage of human failings to 
provide the necessary input to achieve the desired end.

Check out "crashme", "ping of death", and several other examples.  The 
various buffer overflow exploits are a result of both hardware and 
software making assumptions about each other's behavior without doing 
anything to assure it.  Trust but verify is good motto.
>
> Will we ever get past the current hack (instructions+data=computation)?
> Or will we just keep adding fuzz to an arbitrarily rigid model of
> computation?
>
> Robert.

The current model is not the only model.  However, it is quite useful. 
It will endure until it is replaced by something more useful.  It would 
be quite easy (Harvard architecture) to separate instructions from data. 
  I think the truth is that, to my surprise, few give much of a hoot 
about security and reliability.

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The difference between programmable and non-programmable logic--if there is one. Robert Myers <rbmyersusa@gmail.com> - 2011-10-22 19:14 -0400
  Re: The difference between programmable and non-programmable logic--if there is one. Del Cecchi <delcecchi@gmail.com> - 2011-10-22 20:52 -0500
    Re: The difference between programmable and non-programmable logic--if there is one. Andrew Reilly <areilly---@bigpond.net.au> - 2011-10-23 03:06 +0000
      Re: The difference between programmable and non-programmable logic--if there is one. nmm1@cam.ac.uk - 2011-10-23 09:50 +0100
    Re: The difference between programmable and non-programmable logic--if there is one. Quadibloc <jsavard@ecn.ab.ca> - 2011-10-23 09:22 -0700
  Re: The difference between programmable and non-programmable logic--if kenney@cix.compulink.co.uk - 2011-10-23 11:20 -0500
    Re: The difference between programmable and non-programmable logic--if Robert Myers <rbmyersusa@gmail.com> - 2011-10-23 18:23 -0400
      Re: The difference between programmable and non-programmable logic--if Del Cecchi <delcecchi@gmail.com> - 2011-10-23 19:46 -0500
        Re: The difference between programmable and non-programmable logic--if Robert Myers <rbmyersusa@gmail.com> - 2011-10-23 21:27 -0400
      Re: The difference between programmable and non-programmable logic--if torbenm@diku.dk (Torben Ægidius Mogensen) - 2011-10-24 10:36 +0200
        Re: The difference between programmable and non-programmable logic--if Robert Myers <rbmyersusa@gmail.com> - 2011-10-24 19:01 -0400
          Re: The difference between programmable and non-programmable logic--if Robert Myers <rbmyersusa@gmail.com> - 2011-10-24 22:56 -0400
            Re: The difference between programmable and non-programmable logic--if Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-10-25 09:18 +0200
          Re: The difference between programmable and non-programmable logic--if "Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net> - 2011-10-24 21:08 -0700
            Re: The difference between programmable and non-programmable logic--if Mark Thorson <nospam@sonic.net> - 2011-10-25 18:25 -0800
              Re: The difference between programmable and non-programmable logic--if BGB <cr88192@hotmail.com> - 2011-10-25 19:45 -0700
            Re: The difference between programmable and non-programmable logic--if Mark Thorson <nospam@sonic.net> - 2011-10-29 16:39 -0800
              Re: The difference between programmable and non-programmable logic--if BGB <cr88192@hotmail.com> - 2011-10-30 09:54 -0700
                Re: The difference between programmable and non-programmable logic--if Stefan Monnier <monnier@iro.umontreal.ca> - 2011-10-30 13:50 -0400
                Re: The difference between programmable and non-programmable logic--if BGB <cr88192@hotmail.com> - 2011-10-30 15:12 -0700
          Re: The difference between programmable and non-programmable logic--if Del Cecchi <delcecchi@gmail.com> - 2011-10-25 19:53 -0500
            Re: The difference between programmable and non-programmable logic--if Robert Myers <rbmyersusa@gmail.com> - 2011-10-25 21:29 -0400
              Re: The difference between programmable and non-programmable logic--if Quadibloc <jsavard@ecn.ab.ca> - 2011-10-26 08:57 -0700
                Re: The difference between programmable and non-programmable logic--if Robert Myers <rbmyersusa@gmail.com> - 2011-10-26 11:11 -0700
                Re: The difference between programmable and non-programmable logic--if Del Cecchi <delcecchi@gmail.com> - 2011-10-26 16:43 -0500
                Re: The difference between programmable and non-programmable logic--if jacko <jackokring@gmail.com> - 2011-10-26 14:45 -0700
            Re: The difference between programmable and non-programmable logic--if nmm1@cam.ac.uk - 2011-10-26 07:55 +0100
          Re: The difference between programmable and non-programmable logic--if MitchAlsup <MitchAlsup@aol.com> - 2011-10-26 18:03 -0700
            Re: The difference between programmable and non-programmable logic--if Stefan Monnier <monnier@iro.umontreal.ca> - 2011-10-26 21:43 -0400
  Re: The difference between programmable and non-programmable logic--if there is one. Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-10-23 23:28 +0200

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