Where's the cache?

Sorry, this must have been asked and answered 00s of times already, but I can't find it. I downloaded FF 2.0 and auto-updated to FF 2.0.0.1 no problem. No default settings have been altered at all. (I like them as they are.) When surfing there's no usb activity at all (good; everything is very fast) but screen presentation on second and subsequent page visits is not just fast, it's instantaneous. Where are all the pages, images, etc being cached? RAM? the HD? All cached material seems to be wiped on exit from FF ((a) by implication of the settings and (b) because a new FF session shows the same phenomenon: fast page loading on 1st visit, instantaneous on 2nd and subsequent visits).
Thank you.