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PDF Compatibility From: http://www.trevorleverconsulting.com/wp-content/uploads/2014/04/ACT-Compatibility-Chart.pdf From: http://kb.swiftpage.com/app/answers/detail/a_id/23023/~/understanding-act!-compatibility-with-a-microsoft%C2%AE-64-bit-operating-system-and

What does Act! compatibility with a 64-bit operating system mean?
ACT! by Sage 2009 (11.0) and later are compatible with 64-bit operating systems. ACT! 2009 and 
later are not native 64-bit applications, but rather 32-bit applications designed to work with 
64-bit operating systems. This means that you are now able to install and run the Act! application 
on a machine that runs one of the following 64-bit OS versions:
   Windows Server® 2003 SP2
   Windows Server 2008
   Windows Server 2011 SBS (only Act! 2013 and later versions are supported on this OS)
   Windows Server 2012 (only Act! v16 and later versions are supported on this OS)
   Windows Vista®
   Windows 7® (Only ACT! 2010 and later versions are supported on this OS)
NOTE: Microsoft Windows XP 64-bit is NOT supported.