For the first time, Microsoft is releasing Microsoft Office in both 32-bit and 64-bit versions. You will be able to get Office 2010, including Outlook 2010, in 64-bit. 64-bit is not just for servers anymore. Almost any new workstation or notebook these days is built to allow 64-bit OSs and applications.

Overall, 64-bit architecture can use more memory and manage larger datasets. This benefit is greatest for applications with large databases or big file manipulation and computation (video, scientific calculation, 3-D rendering). But you don’t want to make a move to 64-bit Office just because you can. There are many considerations just from the Outlook perspective.

First of all, installing Office 2010 64-bit requires that the underlying Windows OS is also 64-bit. This requires the 64-bit versions of Windows Vista or Windows 7, or even Windows 2003 R2 or Windows Server 2008. Even on 64-bit Windows, Microsoft has made 32-bit the default installation for Office 2010, unless there are 64-bit Office 2010 applications already installed.

All applications within the Office 2010 family must be the same "bitness," including Visio 2010 and Project 2010. If the different applications are installed separately, the subsequent applications must be the same bitness as the first installed. Outlook 2010 must be installed with the same bitness as Excel 2010, for example. If you have any 32-bit Office applications installed, then a 64-bit installation will fail. If you have any 64-bit versions of Office 2010 installed, then additional installations of 32-bit Office 2010 components will return an error.

Third-party applications may pose a problem for administrators who allow users to install Outlook add-ons. Unmanaged Outlook add-on applications that run in their own 32-bit space (a separate .exe) should work fine with 64-bit Outlook if they use the Outlook Object Model to interact with Outlook 2010. MAPI applications and existing managed code add-ons will have to be recompiled to accommodate the 64-bit Outlook.exe process changes. I'll look at the impact of 64-bit on third-party add-ons for Office 2010 in a future article.

Finally, with Office 2010, Microsoft adds a bitness registry key to identify whether the installation is 32-bit or 64-bit. As shown in Figure 1, x64 is the value for the bitness key for a 64-bit installation with the full path reflected in the bottom of the window. The 32-bit installation will show x86 for that value.

For a full list of everything required to assess whether an installation is ready for Office 2010, check out the comprehensive set of articles entitled  "Application compatibility assessment and remediation for Office 2010."