I cannot seem to find any documentation as to whether or not 64-bit background geoprocessing is native to ArcGIS 10.2. Or, is a separate download and install required as in 10.1? There were rumors prior to the 10.2 release that 64-bit background geoprocessing comes pre-installed with the upgrade/download. Is there an authoritative reference on this subject? No relevant system information is available on my Arc Administrator configuration information.
There is an option in the ArcGIS 10.2 Desktop Install for 64bit background Geo-Processing.
In response to the answer which suggests to turn off background geoprocessing, I will just mention that if you do this you will negate the very purpose of the 64-Bit Geoprocessing installation. In order to take advantage of the 64-bit capability that this installation offers, you MUST have background geoprocessing turned on. Here are a few quotes (with sources) to back this up:
You can check the General tab of the tool properties for the Always run in foreground check box to see if a tool is capable of running in the background. Source: http://resources.arcgis.com/en/help/main/10.2/index.html#//002100000040000000
To use 64-bit Geoprocessing make sure Background Processing is enabled in the Geoprocessing Options. As long as a tool is capable of running in the background, it will leverage 64-bit processing. Source: http://blogs.esri.com/esri/arcgis/2012/10/31/announcing-64-bit-geoprocessing/
Also, if you are running ArcGIS under 8.1 (not yet officially supported, but it runs), you may want to TURN OFF background geoprocessing as it throws exceptions running tools that work fine when it is turned off. Don't know whether this is an artifact of some as yet unresolved incompatibility with 8.1 that will be fixed down the road.
I had the same problem but did not have the installation setup program that provided me with the screenshot attached in the first answer. Here is a link to the 10.1 service pack 1 that has the option, but I don't know whether this will cause problems when installing on 10.2.