What are the caching mechanisms in NC 1.90?

I asked the question at https://www.nopcommerce.com/boards/t/9133/clear-cache.aspx but the title is not quite relevant so I prefer starting a new one if you don't mind.

I would like to know what are the caching mechanisms provided in nopCommerce 1.90 to optimize the front-end's response time? What types of data are cached (pictures, resources, products pages, ...)?
Does all nopCommerce treatments generate direct SQL queries by default?

Some of you have customized these mechanisms?

Thanks.
Best regards.

Hello,
I could see all the "Cache.*" settings + NopStaticCache and NopRequestCache classes.
Can anyone explain me the overall caching system and the "philosophy" chosen by nopCommerce?
Thanks.

Up ;)