Over the past year, some visitors to the Vault-Co site have mentioned EMP like it was something I had never considered in my design. In fact, solving the EMP problem for the VaultCo Thinkboy has been uppermost in my mind for 10 years. I always figured I would start out with conventional ethernet and work my way to optical cards when they came down in price. Disconnecting ethernet jacks would be standard practice in your pre-attack scenario in any situation.
Let's assume that our Vault-Co Thinkboy OS running under DOS 16 bits has only two lines coming into it ... one for Ethernet (currently intended to carry only IPX packets initially for all inter-terminal communications) and another running off a serial port for the I2C controller. I have not got around to building my relay controller kit yet intended for the parallel port but I can always connect that to I2C as well. So that's two lines only coming into the machine to carry EMF, lightning current or the electromagnetic shockwave of an EMP burst. That would be the only connections your machine is running to anything in the outside world. If you baffle these with optical connections, your chances of EMP damage to your network dedicated machines drops to zero or pretty close thereof. I intend to run traditional ethernet cable aboveground between different stations in my shelter but all of these will terminate in optical adapters.
I just bought 2 of the PCI optical ethernet cards pictured above off EBay from a local Australian dealer for $4.00 apiece. A short while back these would run you $100.00 apiece easy.
The only gray area is getting them to run the LANDOS packet driver correctly, but their specification claims it is tested with both that driver and the MS network DOS drivers.
As for baffling the serial port optically, this is a $5.00 solution involving a circuit some people can build from scrap parts in twenty minutes. As soon as I find a good solid design schematic for serial optical I will post it.