>"Way back in the 70s when I was building logic circuits, I was warned repeatedly that I'd have to get a few things right, or risk "locking up" or "burning out"

>"Way back in the 70s when I was building logic circuits, I was warned repeatedly that I'd have to get a few things right, or risk "locking up" or "burning out" the CMOS chips I was using. The bogeyman was "Signal Reflection", but no one could tell me what it was, or why it was so bad." [...] >"I remember hooking up a television, again, back in the 70s, and we had to change the cable connecting the aerial, because it was 75-Ohm, and we needed to use 300-Ohm. I was confused. It was wire, and certainly if you connected a meter to measure the resistance, you didn't get 75 Ohms, or 300 Ohms. You got effectively 0 Ohms. It was wire, after all, and wire didn't have resistance. No, but it has impedance. When you have a current flowing down the wire, you have electrons in motion (although not as much as you may think!). And if you have a moving charge, you have a magnetic field. So when you start the current, it starts to create the [temporarily changing] magnetic field, and a changing magnetic field creates a voltage in the opposite direction. So that opposes the current, giving a dynamic [instantaneous] resistance. So starting the current off down the wire causes a [instantaneous] resistance, and we can then talk about how much resistance we experience. That depends on a lot of things, but it serves to show that even just current on a wire is a complex thing." Observation: Changing the current in an existing circuit might not result in an instantaneous change in the current -- that's because an instantaneous change in current results in a instantaneous change in the magnetic field surrounding the current, and an instantaneous change in the magnetic field surrounding a current may in turn act to influence the exact amount of current which can be carried in an infinitesimally short time period... Over a very short, but not instantaneous amount of time, these forces balance, and the current does indeed flow, but that does not happen in an instantaneous / infintesimally small - unit of time... Fascinating!