While looking at SATA, PCIe, USB, SD UHS-II it struck me that they are all the same: digital serial bitstream, transmitted using differential pairs (usually 8b/10b coded), with some differences in link/protocol layers.
Why so? Why did this become the standard?
Why are there no widespread system communication protocols that heavily employ some advanced modulation methods for a better symbol rate? Am I missing something? This is not a question of "serial vs parallel" but a question of "digital signaling vs modulated analog"
Answer
Why there are no widespread system communication protocols that heavily employ some advanced modulation methods for a better symbol rate?
If the basic copper connection between two points supports a digital bit rate that is in excess of the data rate needed to be transmitted by the "application", then why bother with anything else other than standard differential high-speed signalling?
Employing an advanced modulation scheme is usually done when the "channel" has a bandwidth that is much more limited than copper or fibre.
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