Summary:

For most versions of Internet Explorer, the 32-bit version of the browser has to be run in order to use 32-bit ActiveX controls. IE 10 allows the running of 32-bit ActiveX controls in a 64-bit process.

More information:

All 64-bit versions of Windows are capable of running Internet Explorer in 32-bit or 64-bit mode. When using IE, several CRM features (such as the Document Drop and CTI) are dependant on using ActiveX controls. All Sage CRM ActiveX controls are 32-bit.

Earlier versions of Internet Explorer (up to and including IE 9) could only run 32-bit ActiveX controls in a 32-bit browser process. When using the 64-bit version of Internet Explorer, the Sage CRM ActiveX controls would not load.

Sage CRM has supported IE 10 since the release of v7.1g.

With the release of Internet Explorer 10, Microsoft introduced support for 32-bit ActiveX controls in 64-bit IE processes.

http://blogs.msdn.com/b/ieinternals/archive/2012/03/23/understanding-ie10-enhanced-protected-mode-network-security-addons-cookies-metro-desktop.aspx

"In Internet Explorer on the Desktop, by default, Content Processes remain at 32bit by default for compatibility with 32bit ActiveX controls, Toolbars, BHOs, etc. Even when you directly launch the 64bit iexplore.exe executable, you will still have a 64bit Manager Process that hosts only 32bit Content Processes. If you want to enable 64bit Content Processes for the Desktop, you must tick the Enable Enhanced Protected Mode option in the Security section of Internet Explorer’s Tools > Internet Options > Advanced tab. When this option is enabled, all Content Processes that are running in Protected Mode (e.g. Internet Zone and Restricted Zone, by default) will begin to use 64bit Content Processes."

The functionality allows the Sage CRM ActiveX controls to be run in a 64-bit IE 10 process. The compatibility matrix will be updated to reflect this in a forthcoming release.