I think it's also worth linking to David Beazley's Curious Course on Coroutines and Concurrency [1]. It's exploring the ideas of a task scheduler implemented in Python. This article reminded me of it. It's not a full VM, but about half way into the PDF he goes into quite some detail on how to build a task scheduler modelled after an OS and how it works in an actual OS. Give it a read.

[1] http://www.dabeaz.com/coroutines/