[eqvinox]

I'd highly advise against using GHz here (without further context, at least), a 32Gbaud / 32Gsym/s NRZ signal toggling at full rate is only a 16GHz square wave.

baud seems out of fashion, sym/s is pretty clear & unambiguous.

(And if you're talking channel bandwidth, that needs clarification)

[kvemkon]

> > I think Gen7 used 32GHz, which is ridiculously high.

> 16GHz square wave

Is it for PCIe 5.0? PCIe 6.0 should operate on the same frequency and doubling the bandwidth by using PAM4. If PCIe 7.0 doubled the bandwidth and is still PAM4, what is the underlying frequency?

[eqvinox]

PCIe 7 = 128 GT/s = 64 Gbaud × PAM-4 = 32 "GHz" (if you alternate extremes on each symbol)

for gen6, halve all numbers

[Dylan16807]

Is it me or are they using the term GigaTransfers wrong? They're counting a single PAM4 pulse as two "transfers".

[eqvinox]

They kinda are and kinda aren't, they're just using their own definition…

(I'm accepting it because "Transfers"/"T" as unit is quite rare outside of PCIe)

[zamalek]

GT/s is also gaining ground for system RAM in order to clear up the ambiguity that DDR causes for end-consumers.

[Dylan16807]

And it's a good way to remove the ambiguity of things like DDR, but ugh "transfers" is not the best word here.

Looking at some documents from Micron I don't see them using GT/s anywhere. And in particular if I go look at their GDDR6X resources because those chips use PAM4, it's all about gigabits per second [per pin]. So for example 6GHz data clock, 12Gbaud, 24Gb/s/pin.

[wtallis]

Aside from GDDR for GPUs, DRAM is still mostly specified with MT/s rather than GT/s, probably because marketing prefers bigger numbers. It'll probably fall off once 5-digit numbers become commonplace.

[guerrilla]

> baud seems out of fashion, sym/s is pretty clear & unambiguous.

Huh? Baud is sym/s.

[eqvinox]

Yes, that was the implication, but I've been getting the impression that using baud is kinda unpopular compared to using sym/s.

[throwway120385]

A lot of people think that baud rate represents bits per second, which it only does in systems where the symbol set is binary. People got it from RS232.

[rbanffy]

IIRC, modems never went much beyond 2400 baud. Everything past that was clever modulation packing more bits onto a single symbol.

[guerrilla]

Huh, I never thought of it that way but you're right.