> Originally, NT kernel was designed for SMP from the ground up, supports asynchronous operations on handles like files and sockets, and since NT 3.5 the kernel includes support for thread pool to dispatch IO completions: https://en.wikipedia.org/wiki/Input/output_completion_port

Say what you will about Microsoft in that era (and there's a lot to be said), the NT kernel team absolutely crushed it for their customers' use cases. IOCP were years ahead of anything else.

I pretty much hated all of the userspace Win32 work I did (MIDL, COM, DCOM, UGGGGGGGGH), but the Kernel interfaces were wonderful to code against. To this day I have fond memories of Jeffrey Richter's book.

It's not enough to have a nicish abstraction, how did it work in practice and eek out performance? I've heard Bryan Cantrell say there wasn't much there and would be curious to really know what the truth is and more explanation on both sides.