Differentiate the numbers as either data or instructions

"karthikbalaguru" <karthikbalaguru79@gmail.com> wrote in message 
news:1192956657.375752.263790@t8g2000prg.googlegroups.com...
> Hi,
>
> How is a processor able to differentiate the numbers as either data or
> instructions ?

For the most popular computers today... it doesn't.

Computers store numbers in addressed locations in memory.  When the "program 
counter" is set to an address and the processor executes the number at the 
address, it is an instruction.  When a program loads a value from the same 
address into a processor register, it is data.

But generally speaking if you look at a number somewhere in memory you can't 
tell whether it is data or an instruction.  It is how the number is used 
that defines it as data or instruction.

Regards,
Steve

>
> Thx in advans,
> Karthik Balaguru
> 

"karthikbalaguru" <karthikbalaguru79@gmail.com> wrote in message 
news:1192956657.375752.263790@t8g2000prg.googlegroups.com...
> Hi,
>
> How is a processor able to differentiate the numbers as either data or
> instructions ?
>
> Thx in advans,
> Karthik Balaguru
>
That is why von neuman is famous and you aren't.  Don't feel bad, I'm not 
either. 

Andrew Smallshaw wrote:
> On 2007-10-21, karthikbalaguru <karthikbalaguru79@gmail.com> wrote:
>> How is a processor able to differentiate the numbers as either data or
>> instructions ?
> 
> In a word, context.  In a Von Neumann architechure, there is no
> fundamental difference between the two.  
-- snip snip

The irony here is delicious.  The original VN architecture
had no address calculation capability - in particular no
index registers.  Treating an instruction as data - adding or
subtracting a value to from its address field was the only
way - other than having a distinct instruction with the
appropriate address in it - to access multiple elements
of an array or other data structure.

As soon as our cousins across the sea invented
address modification registers - b lines - that
was no longer necessary.

To be an effective computer the original VN arch
had to interpret the contents of (some) memory
locations as both instructions and data.

JKA


-- 
How do you tighten a screw? Turn it until the thread strips
and then back it off a quarter of a turn?

In article <L8FSi.34498$c_1.3296@text.news.blueyonder.co.uk>, 
noemail@address.com says...
>
>"karthikbalaguru" <karthikbalaguru79@gmail.com> wrote in message 
>news:1192956657.375752.263790@t8g2000prg.googlegroups.com...
>> Hi,
>>
>> How is a processor able to differentiate the numbers as either data or
>> instructions ?
>>
>> Thx in advans,
>> Karthik Balaguru
>
>
>Some processors have separate data and instruction buses, and some 
>protection mechanisms to generate exceptions, but other than that, it cant 
>differentiate between the two.  It just does with the 'numbers' what your 
>software tells it to do.  If you set the program counter to an address that 
>was within data it would attempt to execute the data.
>-- 
>Regards,
>Richard.


Y'all are forgetting about tagged architectures, which check the tag of the 
memory word before using what was read, or writing to it.  e.g.  Unisys Libra 
series.

		- Tim