4 ms·

> > 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 th

> > 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 1y ago
PCIe 7 = 128 GT/s = 64 Gbaud × PAM-4 = 32 "GHz" (if you alternate extremes on each symbol) for gen6, halve all numbers
- Dylan16807 1y ago
  Is it me or are they using the term GigaTransfers wrong? They're counting a single PAM4 pulse as two "transfers".
  - eqvinox 1y ago
    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 1y ago
      GT/s is also gaining ground for system RAM in order to clear up the ambiguity that DDR causes for end-consumers.
      - Dylan16807 1y ago
        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.
        mjevans 1y ago
        Would you rather go back to the modem days and call a 'Transfer' a 'Baud'? PAM encoding is already analog, and also correspondingly more expensive (power, silicon size, etc) for the increase in speed. It really wouldn't surprise me if even on workstation platforms only a subset of core lanes were Gen6+ and the common slots were redriven Gen5 or less off of a router / switch chip.
        Dylan16807 1y ago
        > Would you rather go back to the modem days and call a 'Transfer' a 'Baud'? We don't have to go back, baud is still in use. I would expect transfers per second to be a synonym for baud though, and for bits per second per pin to use a different word.
      - wtallis 1y ago
        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.

eqvinox 1y ago

PCIe 7 = 128 GT/s = 64 Gbaud × PAM-4 = 32 "GHz" (if you alternate extremes on each symbol) for gen6, halve all numbers

Dylan16807 1y ago
Is it me or are they using the term GigaTransfers wrong? They're counting a single PAM4 pulse as two "transfers".
- eqvinox 1y ago
  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 1y ago
    GT/s is also gaining ground for system RAM in order to clear up the ambiguity that DDR causes for end-consumers.
    - Dylan16807 1y ago
      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.
      - mjevans 1y ago
        Would you rather go back to the modem days and call a 'Transfer' a 'Baud'? PAM encoding is already analog, and also correspondingly more expensive (power, silicon size, etc) for the increase in speed. It really wouldn't surprise me if even on workstation platforms only a subset of core lanes were Gen6+ and the common slots were redriven Gen5 or less off of a router / switch chip.
        Dylan16807 1y ago
        > Would you rather go back to the modem days and call a 'Transfer' a 'Baud'? We don't have to go back, baud is still in use. I would expect transfers per second to be a synonym for baud though, and for bits per second per pin to use a different word.
    - wtallis 1y ago
      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.