That's more or less explains it all and I partly agree with it. Whatever they choose to upgrade it to, I just hope they don't connect systems to internet.
A hacker explains why US nukes controlled by ancient computers is actually a good thing http://uk.businessinsider.com/hacker-us-nukes-report-2016-5
OS used is probably EDX or MTM. Internet for all practical purposes didn't exist when the Series 1 was in wide use. Just might be one of the securest systems on the planet presently. BTW- for real-time and I mean in "real time" not time sliced, the Series 1 was tops for what it could monitor.
