Most developer workstations have had SSDs for many years. This applies to the Windows 10 developers, too. So they haven't paid any real attention to performance regressions on HDDs, since it still works. It's just slow. But it's a HDD so who cares?

That means there's now a lot of I/O going on before and after login, more than would have ever been tolerated in the "old days". Yes, initial boot is just streaming reads, that's easy. But once the OS gets going, it starts logging things... writing. Or finishing up the dregs of the last system update. And NAND SSDs do not handle that mix well at all. They do extremely well with all-reads and very well with all-writes, but a mix will bog them down (block granularity? I don't know why).

Optane doesn't do that. It doesn't care about reads versus writes, or small writes between larger reads. It just goes, and it responds fast no matter what the mix.

It's not really the sort of thing where you notice "wow, this is so fast". It's the sort of thing where you notice randomly sometime that "hey, I've never actually had to wait for this disk". It's harder to notice the absence of pain compared to the pain itself. With Optane, something else is always the bottleneck.

It's not a huge effect, but it was pretty easy to justify the smaller price premium for Optane a few years ago when it was introduced. I fully expected it would carve out a bigger niche for itself at the top of the performance market -- because it really is the top, ahead of anything NAND -- but that hasn't happened. More Intel failings, I guess.