This article discusses using APC or OPcache with Drupal.
The Alternative PHP Cache (APC) and OPcache provide opcode caching. By caching the compiled operation codes (opcodes) of PHP scripts, APC and OPcache enable sites to serve page content significantly faster.
APC is a PHP extension that runs on PHP 5.4 and earlier versions. Because it is a separate extension, it may or may not already be installed on your server. For information about how to determine if APC is installed on your server, please see this article.
OPcache is a drop-in replacement for APC that runs on PHP 5.5 and later versions. OPcache is a core component built into PHP, so it does not require separate installation like APC does.
When APC or OPcache is installed on your server, no additional configuration is required on your part. APC and OPcache work at the web server level, so Drupal itself does not require any special configuration to take advantage of the performance benefits.