If backward compatibility with the applicable parts of APC is required, APCu must be configured with the option --enable-apcu-bc.
Warning PHP 7 has a separate module (» apc.so) for backwards compatibility with APC.
In backward compatibility mode, APCu registers the applicable APC functions with backward compatible prototypes.
Where an APC function accepted
cache_type, it is simply
ignored by the backward compatible version, and omitted from the prototype for
the APCu version.
On Windows, APCu needs a temp path to exist, and be writable by the web server. It checks the TMP, TEMP and USERPROFILE environment variables in that order and finally tries the WINDOWS directory if none of those are set.
For more in-depth, highly technical implementation details, see the [https://git.php.net/?p=pecl/caching/apc.git;a=blob;f=TECHNOTES.txt » developer-supplied TECHNOTES file] .
APCu sources can be found » here.