APCu is userland caching: APC stripped of opcode caching in
preparation for the deployment of Zend Optimizer+ as the
primary solution to opcode caching in future versions of PHP.

APCu only supports userland caching (and dumping) of variables,
providing an upgrade path for the future. When O+ takes over,
many will be tempted to use 3rd party solutions to userland
caching, possibly even distributed solutions; this would be a
grave error. The tried and tested APC codebase provides far
superior support for local storage of PHP variables.