Optical PCIe 7.0 connection hits 128 GT/s

GT/s = gigatranfers per second.

What's a transfer? That like a packet or a single bit?

One bit, but it's a bit of the underlying signal layer which has a 1-2% redundancy over the actual data. PCIe 2.0 and earlier encode 8b data in 10b signal. 3.0 to 5.0 encode 128b data in 130b signal. 6.0 and 7.0 do a more complicated thing: https://pcisig.com/blog/pcie%C2%AE-60-specification-webinar-...

Also the speed is per lane, eg an x8 slot / port / device is called that because it has 8 lanes, which all transfer in parallel.

So, it's still bits all the way down? Whether we're talking about app, IP, or LL it's always bits/s, each level bringing a cost due to encapsulation. And then at PHY there's baud.

Is non-ISO unit "T" / "transfer" a marketing term or really specialised jargon? "transfer" just doesn't click in my mind, at best "a transfer" (countable) is about moving a sizeable aggregate chunk that has some semantic meaning, not a single fundamental quantum of information.

Unrelated: "gigatesla per second" is such a mind-boggling unit.

It's really specialized jargon that underscores the fact that it's raw bandwidth, not usable bandwidth.