[Simh] A terminology question

[Leo Broukhis]

That's right. An attempt to execute a word with anything but "command
convolution" results in an exception. There were system calls ("extracodes"
in BESM-6 parlance) to store individual words as instructions and to switch
store mode back and forth.

Leo

On Wed, Feb 11, 2015 at 12:23 AM, Pontus Pihlgren <pontus at update.uu.se>
wrote:

> If I understand it correctly, you have four combinations:
>
> 11 -- illegal
> 10 -- data
> 01 -- instruction
> 00 -- illegal
>
> And memory locations market illegal or data wont be executed?
>
> This reminds me of the more modern terms "DEP" - Data Execution
> Prevention, "NX" - No-eXecute, "XD" - eXecute Disable, "XN" - eXecute
> Never. DEP and NX seems to be a generic terms and the others are
> platform specific. Different OSs that take advantage of this calls it
> different things.
>
> Not quite the same as the DEP is usually enforced on memory pages.
>
> /P
>
> On Mon, Feb 09, 2015 at 12:32:47PM -0800, Leo Broukhis wrote:
> > Dear colleagues,
> >
> > There is an implementation detail in the BESM-6 architecture the name of
> > which we've struggled to translate adequately.  There is a feature
> > preventing execution of arbitrary data as instructions implemented using
> > two parity bits per word, for the upper and the lower half-word. The
> > overall parity must be odd, and one of the valid parity bit
> configurations
> > denotes an instruction, and the other denotes data. In the original
> > documentation this mechanism was called
> >
> https://translate.google.com/#ru/en/%D1%81%D0%B2%D0%B5%D1%80%D1%82%D0%BA%D0%B0
> > (the two forms were called literally "command convolution" and "number
> > convolution").
> >
> > Unlike a tagged architecture, there isn't a fixed tag value to indicate
> > instructions or data.
> >
> > Is there a standard term for this? "Convolution" sounds too mathematical.
> >
> > Thanks,
> > Leo
>
> > _______________________________________________
> > Simh mailing list
> > Simh at trailing-edge.com
> > http://mailman.trailing-edge.com/mailman/listinfo/simh
>
>
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