[jhallenworld]

Well nvDIMMs are available right now (from companies like Netlist, Agigatech, Viking, Smart, Micron). This is DRAM with an analog switch, a controller and flash memory. When you lose power, the DRAM is disconnected from the processor and the contents are copied to the flash. The newer technology might be cheaper, but I thought so far the write performance is not as good as DRAM.

The issue is the cache: the data is not non-volatile until it has been written back to DRAM. Even then, you need some advanced warning of a power outage for it all to work.

Unibus (bus for PDP-11 core memory systems) had an early warning signal, to give the memory controller a chance to write back the previous (destructive) read.