The Optane 16GB and 32GB drives are designed to act as cache while the 900P drives are designed to be standalone SSDs leveraging the same storage technology used in the much smaller cache drives. I wondered if the Optane caching software would recognize a 900P as a cache drive due to them being based on the same technology. I asked Intel about this and one expert said no while another said that he had no idea but it certainly was not the intention and would not be intentionally supported if it did work. Hearing this I of course had to try it and to my surprise, it worked flawlessly. The back story on this is that I was building a system for someone that wanted top of the line disk access with 4TB of space, they also did not want to mess with RAID or multiple drive letters or drives mounted as folders. They wanted a single large drive that was stupidly fast. You can certainly cache a SATA SSD to the 16/32GB Optane cache drives but that really does not get you much, especially when it comes to writes and 32 gigs is a very small fraction of 4TB. The 900P by contrast is huge and outperforms the 16/32GB models handily. Understandably this is a corner case and is too expensive to be "worth it" but if you have $ to burn and want a 4TB Optane SSD today this gets you pretty damn close to that.