Actually BX was around in the late 1800s. It was used to add receptacles to knob and tube systems before NM sheathed cable, or Romex, was around. I've seen many variations of the old romex, mostly cloth covered, some with a spiraled cardboard insulator inside the cloth followed by rubber on the wires. Some of the cloth type is impregnated with asphalt or tar. I've also seen lead sheathed romex. The latest cloth covered type has plastic insulation on the wires. All the folks I know just call it two wire romex.
Theres an excellent book called "Old Electrical Wiring" by David Shapiro which explains it all.
