Non-volatile memories like NAND flash and Intel's 3D XPoint have fundamental advantages over DRAM that guarantee they'll be cheaper than DRAM. DRAM requires a transistor for every memory cell, and stores one bit per cell. Non-volatile memories like NAND flash and 3D XPoint don't need an extra transistor to isolate each memory cell, which frees them up to be built with multiple layers per die, and the non-volatility is key to their ability to store more than one bit per memory cell (though the currently-shipping 3D XPoint is only storing one bit per cell).

So the non-volatility is indirectly related to why those memories are more cost-effective than DRAM, but they still have the array structure that allows for much lower access times than a hard drive.

> like NAND flash

This has been in SSDs for long enough without being hailed as a game changer, which is why I question anything common between the two that appears to be called out as the cause.

> Intel's 3D XPoint have fundamental advantages over DRAM that guarantee they'll be cheaper

This may be true for the producer, but in a monopoly situation, one could reasonably expect any savings will be collected as profit rather than passed on to the consumer.

> This has been in SSDs for long enough without being hailed as a game changer, which is why I question anything common between the two that appears to be called out as the cause.

It's only been in the past few years that flash memory has been accessed through interfaces that weren't made for hard drives. NVMe is recent enough that it's no surprise to see that the conservative, slow-evolving OS virtual memory subsystem still hasn't been entirely re-architected to account for the new possibilities that fast, low-latency storage brings.

> It's only been in the past few years that flash memory has been accessed through interfaces that weren't made for hard drives.

Just how few years are we talking about? From what I recall, Fusion-IO's model didn't use a hard disk interface, and their products were in the sub-millisecond latency range over 6 years ago, maybe even a full decade.

At the time (and more or less continuously since then), I've questioned why anyone would want to pay such a huge premium over disk-imitating flash (that is, enough of it to match the storage, throughput, and IOPS).

Low latency would be a credible explanation, although I don't recall anything in the way of even benchmarks showing the difference with real-world software like a database.

All that said, unless I'm missing something like an order of magnitude drop in latency, I'm wondering why.. this time it's different?