cpu - How instructions are differentiated from data?

Question

While reading ARM core document, I got this doubt. How does the CPU differentiate the read data from data bus, whether to execute it as an instruction or as a data that it can operate upon?

Refer to the excerpt from the document -

"Data enters the processor core through the Data bus. The data may be an instruction to execute or a data item."

Thanks in advance for enlightening me! /MS

Answer 1

Simple answer - it doesn't. Machine code instructions are just binary numbers, as are data. More complicated answer - your processor may (or may not) provide segmentation of memory, meaning that attempting to execute what has been specified as data causes a trap of some sort. This is one of the the meaning of a "segmentation fault" - the processor tried to execute something that was not labelled as being executable code.