What loads the server the most?

Question

PHP

The site includes CSS, PHP, JavaScript. When accessed, the load seems to be 90%. And yet, when two pages refer to the same CSS table, does it load every time or are the styles hanging somewhere?

Answer 1

Loading what? Processor?
Returning css and javascript does not load the processor in any way.
PHP hypothetically can (if you have mega complex calculations or crooked code) and SQL of course (again, in the case of crooked code or huge tables)

Answer 2

CSS / JS / HTML - they work on the side of the user's browser (client languages), your server simply gives them away and that's all, they cannot load the server in any way if the chi is not 100500 with 100500 mb.
php - as written above,
mysql can - it usually loads the server, depending on how queries are made and indexes are placed.

Answer 3

When there are many requests for statics, the disk subsystem may not be able to cope.
There may be too many simultaneous queries to the database (this is the most common).
Maybe there is not enough RAM and the server climbs into the swap.