Here&#x27;s my tl;dr:<p>1. Interix&#x2F;SUA subsystem was not developed by Microsoft.  It was acquired from a company called Softway.  It was used internally to transition Hotmail from FreeBSD to Windows.  It is believed some important MS customers also made use of Interix and possibly came to rely on it.<p>2. How to explain MS seeming ambivlance toward a POSIX layer on top of Windows?  Idea: Windows API is so complex (convoluted?) as to exclude competition.  See Joel On Software reference.  He marvels at Windows&#x27; backwards compatibility - being able to run yesterday&#x27;s software on today&#x27;s computers.  Yet he also admits MS strategically developed software that would not run on today&#x27;s hardware, but only on tomorrow&#x27;s.  (Not intending to single out MS as I know other large companies in the software business did this too.)<p>Complexity as a defensive strategy.  Who would have guessed?<p>Many years ago, I gave up on Windows in favor of what I perceived as a more simple, volunteer-run UNIX-like OS that was better suited to networking.<p>As it happens, unlike Windows, _all versions_ of this OS run reliably on most <i>older hardware</i>.  Although it was not why I switched at the time, I have come to expect that by virtue of the UNIX-like OS, my applications will now run on older <i>as well as</i> current hardware.  I rely on this compatibility.<p>Unlike Windows I can run the latest version of the OS on the older hardware.<p>Windows backwards compatibility is no doubt worthy of praise, however the above mentioned compatibility with older hardware is more important to me than having older software run reliably on a proprietary OS that constantly requires newer hardware.<p>The 2004 reference Reiter cites on the &quot;API War&quot; suggests people buy computers based on what applications they will be able to run.<p>Unlike the reference, I cannot pretend to know why others buy certain computers.  Personally, I buy computers based on what OS they will be able to run.  Traditionally, in the days of PC&#x27;s and before so-called smartphones, if you were a Windows user this was almost a non-issue.  It was pre-installed everywhere.<p>At least with respect to so-called smartphones it appears this has begun to change.  Maybe others are choosing to buy computers based on the OS the computer can run?  I don&#x27;t know for sure.<p>As for the &quot;developers, developers, developers&quot; and availability of applications idea, since switching to UNIX-like OS, being able to run any applications I may need has been a given.  In fact, I have come to rely on applications that will only run on UNIX-like OS!<p>And now it seems MS is going to make running UNIX applications on Windows easier.  Why?<p>As with Interix, will the reasoning behind this successor POSIX layer remain a mystery?