title: Detect 64-bit or 32-bit Windows from User Agent or Javascript?
body: <p>I want to offer the right version of a download.  The versions I have are:</p>
  
  <ul>
  <li>32-bit Windows</li>
  <li>64-bit Windows</li>
  <li>Linux</li>
  </ul>
  
  <p>Detecting Linux using the User Agent field is easy; but is it possible to reliably figure out if Windows is 32-bit or 64-bit?</p>
  
  <p>Users might be using weird browsers - IE and Firefox are common, and we probably have an Opera user somewhere; maybe a Chrome user too.  I know that 64-bit Windows 7 ships with 32-bit and 64-bit versions of IE, and I'd like to send them both the 64-bit version of my download.</p>
  
  <p>(Edited to add: I know that I should provide all the options, and I will.  But <a href="http://www.joelonsoftware.com/uibook/chapters/fog0000000062.html" rel="noreferrer">people don't read the options</a>.  So I wanted to provide the right download by default, to improve usability.  Of course, while this is helpful if I get it right, it's extremely unhelpful if I get it wrong.  And from the answers so far, it doesn't look like there's a reliable way of doing this).</p>