Threads were introduced in UNIVAC 1108 EXEC 8, first demoed in 1967 and running in production from about 1969.  They were called &quot;activities&quot;, but were created with &quot;fork&quot;.   The OS, which ran on multiprocessors, used them internally, and applications could use them as well. EXEC 8 also had synchronous and asynchronous I&#x2F;O (callbacks).  It&#x27;s called OS 2200 today, and still running.<p>When I went from EXEC 8 to UNIX in 1978, my main observation was that the I&#x2F;O was better but the CPU management in UNIX was much worse.