You can see opcache as the big brother of apc cache with is depraced since PHP 5.3
The Zend OpCache provides faster PHP execution through opcode caching and optimization. It improves PHP performance by storing precompiled script bytecode in the shared memory.
How to install OPCACHE on Directadmin
Requirments: Custombuild 2.0 and PHP 5.5 or higher.
./build set opcache yes
Create a .php script to monitor cache hits
Location to change settings of OPCACHE: