[zkms]

My reaction to PCIe gen 8 is essentially "Huh? No, retro data buses are like ISA, PCI, and AGP, right? PCIe Gen 3 and SATA are still pretty new...".

I wonder what modulation order / RF bandwidth they'll be using on the PHY for Gen8. I think Gen7 used 32GHz, which is ridiculously high.

[Dylan16807]

> PCIe Gen 3 and SATA are still pretty new...

That's an interesting thought to look at. PCIe 3 was a while ago, but SATA was nearly a decade before that.

> I wonder what modulation order / RF bandwidth they'll be using on the PHY for Gen8. I think Gen7 used 32GHz, which is ridiculously high.

Wikipedia says it's planned to be PAM4 just like 6 and 7.

Gen 5 and 6 were 32 gigabaud. If 8 is PAM4 it'll be 128 gigabaud...

[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.

[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.

[weinzierl]

Don't forget VESA Local Bus.