Re: IBM VM/CMS
VM was true virtualization, but it was a full OS that provided virtual machines that CMS and guest OSes could run in, rather than a hypervisor. Arguably IBM had hypervisor technology as far back as the mid-60s with CP-40, and even offered it in commercial products (e.g. VMF). But VM/CMS wasn't a hypervisor, strictly speaking - it was a host OS that provided virtual machines. Hypervisors aren't full OSes.
Also, a bit of research has reminded me that CP-67 was commercially released, in a fashion (as an unsupported open-source OS) in the late '60s. The first version of CMS (then the Cambridge Monitor System1, later Conversational Monitor System) ran on CP-67. CP-67 became a project known as CP/370, which was what was released as VM/370 with VM-CMS - a combination generally referred to as VM/CMS. So IBM definitely beats ICL for the "first virtualizing OS" crown.
CMS is basically the shell for VM.
I'm not knocking VM, mind; I have fond memories of using VM/CMS, and VM did a terrific job of virtualizing the system and hosting guest OSes. Basically everyone with more than the smallest IBM mainframe workloads ran it. Even the small software startup I used to work for ran it, so that we could run MVS and VSE to support different product platforms.
1Named for Cambridge, Massachusetts, site of IBM's Cambridge Scientific Center. In the late '80s I worked for another IBM group in the same building as the CSC, though that wasn't the building they were in when CMS was invented, and met some of those CSC folks.
Biting the hand that feeds IT
