Installation
  
   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.
  
  Note: 
   
    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.
   
  
  Note: 
   
    For more in-depth, highly technical implementation details, see the
    » 
     developer-supplied TECHNOTES file
    .
   
  
  
   APCu sources can be found » here.