By Ilya Grigorik on November 13, 2008 Update: post has been renamed to "Parallelism is a Myth in Ruby"... Why? Because concurrency is not parallelism - highly recommend this talk by Rob Pike. Concurrency is the composition of independently executing things (which is possible in Ruby), and parallelism is the simultaneous execution of multiple things (which is not possible in MRI, see below). One is