Windows Server 2003 is considered to be one of the most scalable operating system when running on 64 bit platform. But still there are some consideration which must be consider before migrating SQL Server to 64 bit enviournment

There are some limitations of windows server 2003 which must be addressed before migrating SQL server to 64 bit enviournment

• In 64 bit enviournment, 64-bit programs cannot load and call 32-bit MDAC.
• 64-bit Microsoft Internet Explorer cannot load 32-bit ActiveX controls.
• The 64-bit shell cannot load 32-bit Inproc shell extensions.
• 32-bit installer programs cannot load and register 64-bit DLLs.
• No 16-bit code can run, except for recognized Install Shield and Acme installers (these are hard-coded in Wow64 to allow them to work).
• 16-bit Setup bootstraps are not supported.
• 16-bit MS-DOS and Microsoft Windows 3.x utilities will not start. If you attempt to start such a program, you receive a “Program.exe is not a valid Win32 application” error message.
• There is no support for OS/2 or Posix programs.
• There is no support for Kernel-mode or 32-bit code such as:
  • 32-bit virus-detection or 32-bit file system filters.
  • 32-bit video adapter or 32-bit network adapter drivers.
  • 32-bit Kernel-mode printer drivers.