There are lots of platforms where RAM is tiered, and operating systems that support it. For example, CLX allows for a "NUMA node without CPU" abstraction; ther

There are lots of platforms where RAM is tiered, and operating systems that support it. For example, CLX allows for a "NUMA node without CPU" abstraction; there was a HN article recently about Facebook cooking up their own silicon and Linux patches to implement this so they could expand DDR5 platforms with retired DDR4 memory. Not a new idea...20+ years ago I used mc68k & ns32k BSD systems that had a couple of meg of fast memory onboard and more, slower memory hung off a VMEBus. System tried to keep hot pages in fast memory and it worked reasonably well.