If backward compatibility with the applicable parts
of APC is required, APCu must be configured with the option
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
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.
more in-depth, highly technical implementation details, see the
» developer-supplied TECHNOTES
APCu sources can be found » here.