In low-level #hardware, the binary system means that anything below _x_ Volts will be considered a '0' digit and anything above will be '1'.
Yeah, it can become much more complex, but that is the concept of **binary** inside a processor (and PCM signals too, voltage not being the necessary value to measure).
What if we could have MORE than 2 states, occurring from our measurement? Turns out we can?!
In PAM4 ([Pulse-amplitude modulation](https://en.wikipedia.org/wiki/Pulse-amplitude_modulation)) we have 4 states. You can theoretically define PAM16, if you are not excited yet. The more states you divide your voltage spectrum into, the harder to maintain accuracy and so errors happen. It makes sense, since you are becoming "less binary" and "more analogue"...
Find a way to compensate for the errors in PAM4 and enjoy double the speed of PAM2 (or NRZ for _Non-return-to-zero_).
PCI-e 6.0 will be PAM4. PAM4 is also used in GDDR6X memory (RTX 3080 and 3090) and some high-speed Ethernet standards.
[Image from [Linus Tech Tips](https://www.youtube.com/watch?v=VcrkZigYXak)]
