I remember using early plug and play devices- often I had two devices that both worked, but not if installed in the same machine at the same time, and I would h

I remember using early plug and play devices- often I had two devices that both worked, but not if installed in the same machine at the same time, and I would have to shut down the machine and swap cards to use the other device. I am still not sure exactly that the problem was that caused that.