My first CAD, back in 1984, was a program called "Pallette" was a true 2D draughting program written for "mini computers" (these things in a box about 450mm x450mm x600mm, and ran multiple workstations, with 15 layers and we used it for structural buildings, Architect had some layers, structural had another few, while services had a couple, etc.), and was developed by a couple of engineers in Queensland, Australia.
My first experiance of Autocad was version 2.8, back in 1985/1986, which after "Pallette" was crap, but cheap. Is still crap, but everyone got on the bandwagon early, and can't get off. Serious 3D CAD was run on big computers, (tall cabinets standing in their own airconditioned room, and used via multi screen workstations. When the ship builder I was doing contract work for in 1987, purchased the whole system to design and build some fast catamarans for hydrological surveys in Queensland, this was an American system, full 3D with full electronic output to CNC machines in the workshop, and was concidered an old system then. Came in two fully fitted out containers, one the computer room, the other the workstations.
CAD has been around a lot longer than the PC, and a lot longer than most people think.
Still use at work, mainly Autocad owned programs, Autocad 2015, Autocad 3D civil, Revit 2015, and the quickest way I've found is to import the scanned plan as a simple jpg, or some other picture format, and draw over the top. Scanning to raster/vector, is a waste of time, in my opinion, as then you spend hours and hours 'cleaning' it up, and redoing the text.
cheers
vnkiwi