But that wasn&#x27;t true either at the time of Go 1.1, nor ever I believe. It was the _default_ behavior to have a single core running at a time, but you could just tweak that with the [GOMAXPROCS](<a href="https:&#x2F;&#x2F;godoc.org&#x2F;runtime#GOMAXPROCS" rel="nofollow">https:&#x2F;&#x2F;godoc.org&#x2F;runtime#GOMAXPROCS</a>) variable, documented everywhere.  (That&#x27;s what changed in Go 1.5; now the default for GOMAXPROCS is the number of cores in the machine.)