"Part 1 of this 'Make PHP apps fast, faster, fastest' series demonstrates how you can accelerate your entire site using XCache, a PHP opcode cache. XCache (just one of several caching packages you can evaluate) retains the output of the compilation process, eliminating otherwise redundant work. As long as a page doesn't change, the cached version of the page suffices as proxy. When a page is revised, the cached version is invalidated and replaced.
"An opcode cache--and an opcode optimizer, which is often provided in the same package--is a dirt-cheap technique to hasten the responsiveness of your site. Many cache packages are free and open source, and you need not change any code to realize the benefits..."
