What Is the Oldest, Still Supported OS?

Article note: Neat. I sort of distantly knew Unisys was still supporting the direct ancestors of Burroughs MCP from 1961 as ClearPath MCP - ported through a language change in the 70s and several architecture changes over they years - but you can literally run the direct descendant of MCP as a hosted environment on Windows on commodity x86_64 hardware _as a supported configuration_, and the latest release was just last year.