You may have found a loophole in my specification :) I’d like to amend it to specify that an OS refers to software “that can run...”. (And this is why we do des

You may have found a loophole in my specification :) I’d like to amend it to specify that an OS refers to software “that can run...”. (And this is why we do design reviews!). In your example, a real or virtual machine’s load/setregs interface is an operating system. One that can only run a single program at a time in the case of the physical processor’s bootstrap, but you’d be surprised how similar that is to early DOS. A more hand-waving version is “the lowest level interface over the machine that can run...”. So a processor and a ROM grid can run arbitrary programs, but the lowest common denominator entry point is the ROM flashing spec! A very slow scheduler indeed.