I appreciate the links. I&#x27;m still perplexed though -- isn&#x27;t the Mach component of MacOS X not at all a microkerel? Are you saying &quot;it sort of is&quot;, or &quot;it certainly is&quot; ?<p>The promises of microkernels seem extremely attractive to me, but we know that the promise of simplicity doesn&#x27;t come for free (witness Hurd[0]). There were versions of Mach that were high-profile (i.e.: media&#x2F;developer attention) microkernels, but I thought the Mach in MacOS X really 
was simply &quot;not a microkernel&quot;. Interested to hear more about this if you&#x27;ve got illuminating info.<p>[0] <a href="https:&#x2F;&#x2F;www.gnu.org&#x2F;software&#x2F;hurd&#x2F;hurd.html" rel="nofollow">https:&#x2F;&#x2F;www.gnu.org&#x2F;software&#x2F;hurd&#x2F;hurd.html</a>