Still, it was an amazing achievement for nonetheless relatively affordable PDP-11/45, on which it was eminently usable, and in many ways better than anything else out there aside from it's Multics forefather.
(Originally ran on a first generation PDP-11, later the 11/20, with an extra memory unit so it could run split Instruction and Data (I&D) and have decent budgets for both; on the 11/45, that would be up to 64KiB code, 56KiB data, and 8KiB stack.)
And they ran that system on a machine with 144kB of RAM, where desktop CPUs have had more Level-2 cache than that for years now.
And by now, as somebody else kindly points out, high end server CPUs approach Level 3 caches as big as the hard drive their system ran on... (I think zSeries CPUs have level 3 or level 4 caches in the 128MB range, so their caches actually are bigger than that.)