advance Internet options IE 9 ? please look my question.

When I go to Internet Options and click on the tab "Advanced " and look settings check boxes.

 

I found this 

 

(Enable memory protection to help mitigate onle attacks) but I curious this option only appear on my dell mini 1012 with windows 7 home premium sp1 x32 bits 

 

And when I got check on my Hp Desktop with windows 7 home premium sp1 x64 bits , is not appear this option.

 

already reset advanced settings and do a reset and its not appear . 

 

Somebody know why is this happen?