What really moves PageSpeed Insights: caching, hosting and your stack
The score is the visible end of architecture decisions. Caching, rendering, stacks and hosting compared, and the business results speed has bought.
Performance
Speed and capacity: caching, rendering, server response and what real visitors experience.
How a PHP request actually runs: PHP-FPM, OPcache and timeouts
PHP still starts every request from nothing, as it did in 1995. How nginx, PHP-FPM and OPcache work, and why they explain most PHP performance problems.