Cache the bytecode
Bytecode (called opcode for PHP) is the binary code generated from the source code. Some accelerators are able to cache bytecode, which avoids needing to recompile it from the source code every time. Less time spent compiling equals less CPU and RAM used.
Externalize CSS files and JavaScript
Ensure that CSS files and JavaScript code are separate from the page’s HTML code, with the exception of any configuration variables for JavaScript objects.
If you include CSS or JavaScript code in the body of the HTML file, and it is used for several pages (or even the whole website), then the code must be sent for each page requested by the user, therefore increasing the volume of data sent.
However, if the CSS and JavaScript code are in their own separate files, the browser can avoid requesting them again by storing them in its local cache.
