“Virtualization on the desktop is great, but server-level virtualization has been around for quite a while — Citrix”
You must be a yute, Citrix acquired virtualization relatively recently. VM/CMS is the grandaddy. Around since the ‘80s.
Off by a couple of decades there. IBM's VM OS traces its roots to the 1960s. The original work was done at IBM's Cambridge Labs (which developed the Cambridge Monitor System, CMS) on a modified System/360 Model 40. CP-67 debuted as the first commercial virtual OS a few years later.
A repackaged version for the then-new System/370 machines was released as VM/370 in the early 1970s. All open-source, of course, (long before anyone thought in those terms) since back then software was viewed as a freebie to help sell hardware.