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Retrocomputing

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    Good answer (especially the part about USB, PCIe, SATA, SAS, etc. also being serial.) It might also be worth noting that the term "serial port" is also used commonly to refer to things like SPI and I2C, not just UART. All of those remain common in embedded systems even today. Commented Nov 14, 2017 at 23:46
  • I thought RS232 was only +/- 5v - I seem to recall it was RS422 that was +/- 12v. Commented Nov 15, 2017 at 13:46
  • @reirab Even (wired) ethernet and PCI-e are in essence serial. (With possibly several serial lines used in a parallel). Commented Nov 15, 2017 at 14:05
  • 3
    @OldCurmudgeon TTL RS232 uses 0-5V. RS422 can go upto +/- 48V if memory serves. The 5V and 12V are just very common because those voltages are readily available from the power-supplies of many devices so don't require additional circuitry to generate the voltages. Commented Nov 15, 2017 at 14:08
  • 6
    RS232C is way, way old. I'm Pretty sure that version of the standard required the voltage levels to swing between something like +12V and -12V. Since then we've had RS232-D, -E, and -F. One of the later standards allowed voltage to swiing between +5 and -5 (but still required to accept +12 & -12), and then a still later one allowed it to go as low as +/- 3V. Commented Nov 15, 2017 at 17:36