During my first litespeed server installation, I was asked some questions about php opcode caching. I wasn't sure what it was at the time, so I skipped it. I saw a couple of posts on this site that say pear's "APC" is highly recommended for PHP intensive sites (like mine), that it is stable, and that it works on multiple core processors. What I did not see is any kind of expected improvements. For example, I've seen in many places that LSAPI shows a 30% improvement for a "hello world" PHP program. What exactly is opcode caching doing (perhaps caching compiled versions of the script?) and what kind of performance boost is typical? Has this been quantified anywhere? Benchmarks anywhere? It works on both fastcgi and lsapi versions of PHP? Maybe I'm missing all this stuff, but this particular area doesn't seem to have much documentation.