You can use SMP just fine in Node.js today with <a href="https:&#x2F;&#x2F;nodejs.org&#x2F;api&#x2F;cluster.html" rel="nofollow">https:&#x2F;&#x2F;nodejs.org&#x2F;api&#x2F;cluster.html</a>.<p>The problem with Node.js and concurrency is that everything depends on trusting code to be perfectly written, and that perfectly written code must be written in a naturally confusing callback style that is really easy to screw up.<p>If you do it <i>perfectly</i>, then you get great scalability.  But one bonehead mistake will ruin your concurrency.  By contrast with a pre-emptive model you get decent scalability really easily, but now you&#x27;ve got a million and one possible race conditions that are hard to reason about.<p>This is not a new design tradeoff.  Go back to the days of Windows 3.1 or the old MacOS versions below OS X.  They all used cooperative multi-tasking, just like Node.js.  Today what do we have?  Pre-emptive multi-tasking in Windows, OS X, *nix and iOS.<p>Web development has actually gone back to a model that operating systems abandoned long ago.  As long as your app is small, there is a chance that it will work.  But as your app grows?  Good luck!  (That is why operating systems uniformly wound up choosing hard to debug race conditions over predictably impossible to solve latency problems from cooperative multi-tasking.)