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 <[email protected]> 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 > > [email protected] > > http://mailman.trailing-edge.com/mailman/listinfo/simh > >
_______________________________________________ Simh mailing list [email protected] http://mailman.trailing-edge.com/mailman/listinfo/simh
