title: What does it mean for a program to be 32 or 64 bit?
body: <p>This question: <a href="https://stackoverflow.com/questions/5295903/how-many-bits-does-a-word-contain-in-32-64-bit-os-respectively">How many bits does a WORD contain in 32/64 bit OS respectively?</a>, mentions that word size refers to the bit size of a processor register - which i take to mean the number of bits that a computer processor operates on / i.e. the smallest 'indivisible' amount of bits that a processor operates on.</p>
  
  <p>Is that correct? Using software like Word/Excel/etc, the installers have the option for a 32bit or a 64bit installation. What is the difference?</p>
  
  <p>Since the computer architecture is fixed, it would seem to me that software that is '32 bit' would be designed to align with a computer architecture that has a 32 bit architecture. And a 64 bit program would make efforts to align instruction sets with 64 bit word sizes.</p>
  
  <p>Is that correct?</p>
  
  <p>A very similar question is asked here: <a href="https://stackoverflow.com/questions/19704544/from-a-programming-point-of-view-what-does-it-mean-when-a-program-is-32-or-64-b">From a programming point of view, what does it mean when a program is 32 or 64 bit?</a> - and the accepted answer mentions that the difference is the amount of memory that can be allocated to an application. But this is too vague - unless 32 bit / 64 bit software as a concept is completely unrelated to 32 bit / 64 bit word processor size?</p>