&gt; asynchronous IO architecture only beaten by Solaris asynchronous IO<p>Wait, what?  Event ports are nice, but they&#x27;re still inherently limited by the UNIX &quot;readiness&quot;-oriented I&#x2F;O interface.  And they don&#x27;t provide a unified file&#x2F;socket asynchronous I&#x2F;O interface, either.  (No UNIX does.)<p>VMS got I&#x2F;O right: I&#x2F;O request packets and a completion-oriented I&#x2F;O interface.  This, combined with multiple IRQ levels, is the key element behind Windows&#x27; superior virtual memory management, combined file system cache management and <i>actual</i> asynchronous file I&#x2F;O.<p>Strip everything else away from NT and UNIX and it comes down to buffer-based I&#x2F;O versus packet-based I&#x2F;O (Irps), APCs instead of signals, and multiple IRQ levels (not just hi&#x2F;lo).<p>Side note: AIX copied the NT I&#x2F;O completion port API verbatim.  (Except they ignore the concurrency parameter, which speaks volumes about impedance mismatch between multiple threads and the traditional process-based UNIX IPC model.)<p>Fun quote from Wikipedia -- David Cutler on the UNIX I&#x2F;O model: &quot;getta byte getta byte getta a byte byte byte&quot;.  (<a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Dave_Cutler" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Dave_Cutler</a>)<p>Another tidbit I find interesting: David Cutler was 47 when Bill Gates called him in 1988.  He had been working on OS development in a lead capacity since 1975, and subsequently championed the NT kernel that Gates &quot;bet the company on&quot;.  The core NT APIs that were established in the late 80s and early 90s have stayed the same because they solved the problem correctly the first time &#x27;round.<p>Linux, on the other hand, was started by Linus in the early nineties (when he was in his 20s) &quot;just for fun&quot;.  He implemented enough syscalls to get bash to work and went from there.  At the end of the day, it was still a UNIX-like operating system.<p>Cutler knew UNIX inside out and technically knew where and why it was deficient; VMS and thus NT benefited from that.<p>At the end of the day, it&#x27;s all about the I&#x2F;O, and NT has been dominating that since inception.