Support for 64-bit processors/operating systems
ArcGIS 10.1 on Windows is supported on 64-bit processors and operating systems.
ArcGIS 10.1 for Desktop applications are native 32-bit applications, but take advantage of a technology known as large memory awareness. This means that individual processes may be capable of accessing more than 2GB of memory (up to 4GB) when run on a 64-bit OS.
Some functionality and third-party libraries which are part of ArcGIS are not compatible with large memory awareness, and some portions of ArcGIS may not be able to address more than 2GB even when running on a 64-bit OS.
For a complete listing of supported platforms, see the ArcGIS 10.1 System Requirements page. (Windows 8 and Server 2012 supported at 10.1 SP1.)
ArcGIS for Desktop
ArcGIS 10.1 for Desktop is fully supported on 64-bit (x64) Microsoft versions of Windows operating systems.
ArcGIS Engine 10.1 on windows is a native 32-bit application and is certified running as a 32-bit application on 64-bit (x64) Microsoft Windows. ArcGIS Engine 10.1 is also supported on a Linux 64-bit environment running as a 32-bit application. ArcGIS Engine is also supported on 64-bit Linux Red Hat Enterprise Server (RHELS) 5, (RHELS) 6 and SuSE 11.
ArcReader 10.1 on windows is a native 32-bit application and is certified running as a 32-bit application on 64-bit (x64) Microsoft Windows. ArcReader 10.1 is also supported on a Linux 64-bit environment running as a 32-bit application. ArcReader on 64-bit Linux is supported on Red Hat Enterprise (RHELS) 5, (RHELS) 6 and SuSE 11.
ArcGIS for Server
ArcGIS for Server 10.1 on Windows and Linux (including ArcSDE) is a native 64-bit application at 10.1. It has been certified on 64-bit environments.
ArcGIS License Manager
ArcGIS 10.1 License Manager is a native 32-bit application and is certified running as a 32-bit application on 64-bit (x64) Microsoft Windows, 64-bit Linux environments (RHELS) 5, (RHELS) 6, SuSE 11, and Sun Solaris 10 64-bit.
Background Geoprocessing for ArcGIS for Desktop and ArcGIS Engine
Starting at 10.1 Service Pack 1, 64-bit background geoprocessing for Desktop and Engine will be available. You can install the 64-bit background package for ArcGIS for Desktop or Engine and run your geoprocessing using the 64-bit background processes.
Using 64-bit processing to perform analysis on systems with large amounts of RAM may help when processing large data, which may have otherwise failed in a 32-bit environment. Since all execution is done in the native 64-bit space, more system resources can be used. However. this is not a solution which answers all performance questions. That is because 64-bit background geoprocessing is not always faster, but does scale to provide the ability to crunch large data that may not have been possible before.
This does not change ArcGIS for Desktop with regards to 64-bit support. ArcGIS for Desktop remains a 32-bit application. When geoprocessing tools are executed in the foreground, they will still be executed in 32-bit mode.
Terminal Server Support for 64-bit operating systems
Terminal serving technologies running on 64-bit operating systems are able to provide ArcGIS 10.1 for Desktop applications with up to a 4GB address space.
Intel and AMD processors
ArcGIS 10.1 is supported on both the Intel and AMD 64-bit processor families, such as Xeon64 and AMD64.