| ▲ | zkms 4 days ago |
| 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. |
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| ▲ | Dylan16807 4 days ago | parent | next [-] |
| > 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... |
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| ▲ | eqvinox 4 days ago | parent | prev | next [-] |
| 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) |
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| ▲ | kvemkon 4 days ago | parent | next [-] | | > > 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 4 days ago | parent [-] | | PCIe 7 = 128 GT/s = 64 Gbaud × PAM-4 = 32 "GHz" (if you alternate extremes on each symbol) for gen6, halve all numbers | | |
| ▲ | Dylan16807 4 days ago | parent [-] | | Is it me or are they using the term GigaTransfers wrong? They're counting a single PAM4 pulse as two "transfers". | | |
| ▲ | eqvinox 4 days ago | parent [-] | | 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 4 days ago | parent [-] | | GT/s is also gaining ground for system RAM in order to clear up the ambiguity that DDR causes for end-consumers. | | |
| ▲ | Dylan16807 4 days ago | parent | next [-] | | 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 4 days ago | parent [-] | | 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 4 days ago | parent [-] | | > 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. |
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| ▲ | wtallis 4 days ago | parent | prev [-] | | 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. |
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| ▲ | guerrilla 4 days ago | parent | prev [-] | | > baud seems out of fashion, sym/s is pretty clear & unambiguous. Huh? Baud is sym/s. | | |
| ▲ | eqvinox 4 days ago | parent [-] | | Yes, that was the implication, but I've been getting the impression that using baud is kinda unpopular compared to using sym/s. | | |
| ▲ | throwway120385 4 days ago | parent [-] | | 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 4 days ago | parent [-] | | IIRC, modems never went much beyond 2400 baud. Everything past that was clever modulation packing more bits onto a single symbol. | | |
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| ▲ | weinzierl 4 days ago | parent | prev [-] |
| Don't forget VESA Local Bus. |
