In the spirit of the computer video game Doom and its skill levels, we’ll review a few ways you can improve your Drupal speed performance and optimize for better results and server response time. These tips that we’ll cover may be at times specific to Drupal 6 versions, although you can always learn the best practices from these examples and apply them on your own code base.
If you’re using a Drupal distribution which is great for kick-starting a project with many features built-in, you should still review added modules which are managed through the installation profile as they might prove un-necessary for your product as time goes and your product evolves and matures. Remember that even if you’re not using a distribution, you might have added some modules to meet a functionality, which you no longer use and you disabled through CSS, through the menus, through the theme, but you forgot all about removing the actual module. These un-used modules account for memory footprint as they are loaded through PHP and they can also account for Drupal hooks, which is even worse in terms of performance for you.
Remember to review your installed modules base on Drupal and remove any un-used functionality: