I still remember when Optane was first announced Intel hyped it as a replacement for RAM. When it was finally available it turned out to be about 1,000x slower than RAM and barely faster than other SSD. So much for RAM replacement...
The Optane products released thus far are all literally NVMe SSDs, which is why their best-case latency isn't much better than that of flash-based NVMe SSDs. They still have PCIe and NVMe protocol overhead to deal with, which the 3D XPoint DIMMs won't have.
The unimpressive peak throughput of the current Optane SSDs is largely a consequence of the Optane SSD controller having a fairly low channel count. A single 3D XPoint DIMM will probably have substantially higher throughput than a current Optane SSD.
I also wonder if the current products are bottlenecked by the controller and whether DIMMs will see vastly superior performance. Guess we'll have to wait and see.
There's no question that they are. NVMe drive prototypes that use DRAM as their backing memory instead of flash or some other persistent memory have about the same overall latency as Optane SSDs.
With NVMe, the storage industry is in a much better position to take advantage of 3D XPoint than if we were all still using SATA or SAS, but it's still on a peripheral bus not a memory bus.
Just waiting to see product review, it has the potential to bring In-"Memory" computing to next level.
So GP is right to be concerned about speed for these form factors. If it's not faster than an NVMe drive them it's not worth the price.
NVDIMM-N's have more flash than RAM simply for wear leveling concerns. Micron's 32GB NVDIMM-N has 32GB of RAM and 64GB of flash, but the capacity of the NVDIMM-N is equal to the amount of RAM.
For this first release, "3D XPoint DIMMs will require server platform support because they are unlikely to operate as standard DDR4 DIMMs. The JEDEC NVDIMM-P standard for persistent memory DIMMs has not been finalized and is expected next year".
The answer to your paranthetical depends a bit on how much detail you care for. Both devices are types of resistive crosspoint memories. In XP, the resistor is a chalcogenide that has a low resistance polycrystal line state, and a high resistance amorphous state. These are tuned by the program pulse length.
In TiO2, the mechanism is (presumably, perhaps debatebly) filamentary bridges between electrode, which can be eliminated by reversing the voltage.
So on one level, both are resistive memories. On another, we are comparing a bulk phase transition driven by pulse control to a filamentary transition driven by voltage.
Finally, the more important difference is the selector. PCM devices can use a chalcogenide based threshold switch. That is the OTS on the XP diagrams. That selector is the key to functional, dense memory arrays, and the existance of a matched selector is what makes PCM functional. I haven't seen what the matched selector for memristors is.
Worth reading recent material from Crossbar on these topics.
I didn't really expect that Intel would end up this far ahead of Micron in bringing 3D XPoint to market, but it has been clear for quite a while that Intel has the dominant role in their relationship.
If it were 0.1 second I think life would be quite a bit more pleasant.
I strongly recommend this talk from StrangeLoop on persisted memory: https://youtube.com/watch?v=VE1hCUMLHX4
Are you sure? The article lists a fixed durability of 30 drive writes over 5 years. If it wasn’t wear leveling, those 30 writes would be reached very quickly on specific locations.
Edit: fixing timestamp and adding speaker's name.