On a 64-bit Windows platform, the 32-bit and the 64-bit versions of the PI API can both be installed. On an interface node, 32-bit and 64-bit interfaces may need to be run on the one machine, and the PI API supports this.
The two versions of the PI API are located in different directories, so that the files do not overwrite one another. The PIHOME environment variable defines the location of the 32-bit PI API directory and the PIHOME64 environment variable defines the location of the 64-bit PI API directory.
The different instances of the PI API use different names for the PI API library and DLL, so there are no problems with conflicts of the libraries.