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Optical PCIe 7.0 connection hits 128 GT/s

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204 points WithinReason | 2 comments | 17 Jun 24 11:42 UTC | HN request time: 0s | source
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taneq ◴[17 Jun 24 23:07 UTC] No.40712220[source]▶
GT/s = gigatranfers per second.
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8n4vidtmkvmk ◴[17 Jun 24 23:42 UTC] No.40712523[source]▶
What's a transfer? That like a packet or a single bit?
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Arnavion ◴[17 Jun 24 23:51 UTC] No.40712584[source]▶
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.

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Dylan16807 ◴[18 Jun 24 02:56 UTC] No.40713642[source]▶
> 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

Though the exact details of the overhead don't matter very much. They add 6% extra bits, good enough.

The part I want to call out as complicated/confusing is that a PCIe 7.0 lane puts out a voltage 64 billion times per second, but because each voltage is based on two bits that counts as 128 billion "transfers".

replies(1): >>40714256 #
1. loeg ◴[18 Jun 24 05:11 UTC] No.40714256[source]▶
Yeah, the overhead isn't a big deal now that the overhead is single digit. Back when it was 20% in PCIe 2 it was a much bigger discrepancy.
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2. Dylan16807 ◴[18 Jun 24 05:29 UTC] No.40714333[source]▶
Back then they were adding the overhead on top of the baseline speed, not subtracting it. With 1 and 2 you got the full 1/4 and 1/2 gbps of data per lane, but then 3 was only .985 instead of 1. So I'd argue that 6% for PCIe 6 and 7 is the most meaningful the overhead has ever been.