One reasons for PHP still being considered slow is a consequence of how it works under web server environment: every time a client sends request, application is initialized from scratch - it runs all the bootstrap code. Bootstrapping is repeated over and over again, for every connecting client.
While this is an obvious waste of resources, it is also very difficult to avoid without rewriting an application under different architecture. Is there anything that could be done to at least reduce impact of application bootstrap, without making any changes to actual application? As it turns out, there is.