Davey Shafik has a new post to his site today sharing everything you need to know about opcode caches, the mechanism that's works "behind the scenes" to cache the execution of the opcode paths for later reuse.

Last year I wrote a talk called “Fast, Not Furious: How to Find and Fix Slow Code” - a performance talk covering profiling, memcache and some other stuff. As I often do - to hedge my bets = I stuck a few slides on the end “just in case” I ran through everything too quickly and needed to fill in time. These slides were on APC, the Alternative PHP Cache, and went just a little into tokens and how APC works under the hood. I really enjoyed presenting those 6 slides, and I’ve been wanting to expand on that topic ever since then. Well, after a few weeks of hard work, some input from some great people, including Sara Golemon, Elizabeth Smith and Julien Pauli, I’m so very happy to publish PHP Performance I: Everything You Need to Know About OpCode Caches.

The result is published over on the Engine Yard Developer Center and has been made into a 20 minute screencast (with original slides here). He covers what they are, which ones are out there, the common execution cycle and what happens when the opcodes are cached.