Operating System Limitations - All Platforms
When running in a 64-bit environment, ArcGIS Desktop, ArcGIS Server, ArcGIS Engine, and ArcReader run as a 32-bit application. See Does Esri support 64-bit processors with ArcGIS 10.0 products?
3/4/2015
When running in a 64-bit environment, ArcGIS Desktop, ArcGIS Server, ArcGIS Engine, and ArcReader run as a 32-bit application. See Does Esri support 64-bit processors with ArcGIS 10.0 products?