https://arstechnica.com/gadgets/2018/05/intel-finally-announces-ddr4-memory-made-from-persistent-3d-xpoint/

Ever since Intel and Micron announced 3D XPoint memory in 2015, the world has been waiting for the companies to use it to build memory sticks.

3D XPoint blends the properties of flash storage and DRAM memory. Like flash, it's persistent, retaining its value even when systems are powered down, and it's dense, with about ten times the density of DRAM. Like DRAM, it supports low latency random access. Intel also claimed that its write endurance is substantially better than that of flash. This combination of features created the prospect of memory sticks that look like DIMMs and appear to the system as if they're DDR4 RAM, but with much greater capacities, and with persistence: data written to "RAM" is retained permanently. Memory with these properties is exciting for a wide range of applications—for example, databases that no longer need to concern themselves with flushing data back to disk—and might one day provoke significant changes in the way operating systems and software are designed.