How does the Smarty Cache work exactly in TB 1.5?

[movieseals]

It was quite a hurdle but I managed to upgrade to TB 1.5 from 1.3.  There are still hiccups, mostly with PS modules, but we are mostly there.

Now, because I have been doing a tremendous amount of testing, I needed to clear the cache a lot.  And being both a blessing and a curse, it does not appear to work like I used to expect it.

The new smarty cache menu says it can use the system cache.  Which one does it use?  APCu?  Memcache(d)? Redis?  Does it still work if you do not select one of them in the menu below?  If so, what cache does it use?  If not, why does it not tell you that it will not use the server cache if you do not select anything below?

If system cache is used, why are there files generated in the cache folder?  Why, even if I delete them (like I used to do when I made changes that would not appear), why are there changes that do not appear yet others do.  Stuck in the system cache?  But even clearing the cache does not fix them.  They eventually clear up much later.  I thought it was due to browser cache, but that does not always work either.

Anyways, just trying to understand the logic and what it now uses so that I can flush them better when I try new things.