Maybe the fact that Dave Cutler who was much more a VMS guy that did not liked Unix/Posix at all may have had an influence on the design of the kernel of window

Maybe the fact that Dave Cutler who was much more a VMS guy that did not liked Unix/Posix at all may have had an influence on the design of the kernel of windows NT is an explanation? I must admit I used SFU and IO was all quirkish (buffered IO called in non buffered mode). But knowing that async IO, threading was radically different from POSIX they may have decided at some point that it was not possible to offer a quirkless API for Posix by conflict of construction, and they dropped it. I mean for a lot of programmer an IO is an IO, a process a process... but the kernel may thinks differently. For the record, before I hear the Unix fan boys says that Posix is superior, PyParallel by continium exploits a parallel version of python on windows and have considerable gain from using exactly the heart of Dave Cutler's architecture: multi-threading, async IO... https://speakerdeck.com/trent/parallelizing-the-python-interpreter-the-quest-for-true-multi-core-concurrency https://speakerdeck.com/trent/parallelizing-the-python-inter... I do not say it is the panacea, I say it worths being looked at. As you guess, thinking that the same cause produces the same effect and if the kernel still use Cutlers architecture around multi threading and asyncio then I expect the ubuntu runtime on windows to have quirks around... asyinc io and multithreading.