[0x457]

Not, probably, that just how any "modern" OS works. It also uses RAM as a cache to avoid reads from storage, just like any other modern OS.

Apple uses it for segmentation and nothing else.

Modern being - since the 80s.

[tomxor]

Even on the Atari ST you would use a "RAM disk" when working with "large" data before manually flushing it to a floppy. Some people would use the trashcan icon to emphasise the need to manually flush... Not quite a cache, but the concept was there.