It's between RAM and SSD. Much closer to RAM speeds but data persists after turning off power. Biggest advantage over just being a faster disk is that it's byte-addressable random access like memory, so you don't have to deal with writing pages/blocks to drives.

The throughput and latency is fast enough that many apps can skip using memory and work straight from this. We already see this in some mobile devices that only have solid state and instant boot times because the data is always ready, with no need to shift from disk to ram.

It'll be awhile before OS and applications take advantage but it has potential to be a major shift in how storage works.

Disclosure: I work on Google Cloud.

NVMe is (now) a more general purpose "speak to flash like things". This Optane memory stuff is made of "flash", but unlike our Local SSD offering (or AWS's i3) it's at a latency and throughput closer to DRAM.

Despite it being marketing material, I find the pyramid diagram [1] helpful. This blog post is about "Optane Persistent Memory".

[1] https://newsroom.intel.com/wp-content/uploads/sites/11/2018/...

A better comparison would be EC2 x1 instances which are high memory instances designed for SAP HANA like these ones: https://aws.amazon.com/ec2/instance-types/x1/