System Resources versus RAM

A few days ago there was interesting thread discussing what System Resources
are. A couple of posters pointed out that System Resources, while it is a
special type of memory, isn't the same as RAM.

However, no one, as far as I could tell, said what is the relationship, if
any, between SR and RAM.

Also, how can you find out how much available RAM there is on your machine
as distinct from SR? The Performance tab only shows SR.

Or does that not matter, since only System Resources matters as far as the
machine's ability to function is concerned?

Or let's put it this way: Why does available SR matter more than available
RAM?

Larry