Intel Teases Thunderbolt 4, Light On Detailsby Ganesh T S on January 7, 2020 1:03 PM EST
- Posted in
- Trade Shows
- Thunderbolt 3
- CES 2020
- Thunderbolt 4
Intel demonstrated a Tiger Lake system on stage in their CES 2020 keynote yesterday. One of the interesting aspects was the teaser of Thunderbolt 4, with a mention of it offering four times the speed of USB 3. After reaching out to Intel for additional details, it appears that they are not ready yet to share more information.
Intel did confirm that that they were referencing USB 3.2 Gen 2 - the 10 Gbps version - in the keynote presentation. This means that the peak speeds (40 Gbps) are not changing relative to Thunderbolt 3. Given that the Thunderbolt 3 specifications have been donated to USB-IF for USB 4.0, it appears likely that Thunderbolt 4 may be a push for Intel certification of certain Type-C ports. We look forward to receiving more concrete information from Intel regarding the new features, if any, in Thunderbolt 4.
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boeush - Tuesday, January 7, 2020 - linkAt some point soon, the ports themselves will just have to become optical (at least for the data-carrying component, apart from any "hybridized" power delivery.) That'd make for cheaper cables...
Post-PCIe4, the bus itself might have to switch to an optical implementation. Hopefully, silicon photonics will have finally reached a sufficient level of maturity, power efficiency, and manufacturing readiness a few years from now (there's not much time left before we start hitting serious roadblocks in power dissipation and performance, with current tech...)
brakdoo - Tuesday, January 7, 2020 - linkYou don't need silicon photonics for 80gbps. For 100 gbps Ethernet we already have very cheap VCSEL (4x25 as cwdm or multiple fiber cable). 100gbps transceiver are available for US$ 99.00
now with all the overkill that Ethernet transceivers have (like management I2C).
repoman27 - Tuesday, January 7, 2020 - linkThunderbolt is 2x20 though, and can't easily go wider. 40 Gbit/s over copper is totally doable, at a lower cost and using less power than optical transceivers for the sub 5m lengths that are required, but PAM4 and FEC are almost certainly going to be necessary.
repoman27 - Tuesday, January 7, 2020 - linkThunderbolt 3 is *already* operating 29% faster than PCIe Gen4 (20.625 GT/s vs 16 GT/s). 80 Gbit/s Thunderbolt will require PAM4 signaling.
crimsonson - Tuesday, January 7, 2020 - linkI think you mean "32 Gb" and not 22 Gb. 8Gb is reserved for video signal, inaccessible to data transport.
repoman27 - Thursday, January 9, 2020 - linkNothing is reserved for anything.
PCIe Gen3 x4 is four lanes at 8 GT/s with 128b/130b encoding leaving ~31.5 Gbit/s for the upper layers. Like all packet based protocols, there is also protocol overhead. With a TLP maximum payload size of 128 B (which is what Thunderbolt uses), the upper limit for throughput once you remove all the framing, packet headers, and error correction code is ~27.25 Gbit/s or 3406 MB/s. That's for 100% maximum payload size packets without any retransmits or intervening DLLPs, so real-world throughput will necessarily be lower.
Thunderbolt storage benchmarks top out around 22.5 Gbit/s or 2812 MB/s which is 17.4% lower than the theoretical maximum. Looking through the USB4 specification, my best guess is that the observed discrepancy is due to the considerable latency involved in Thunderbolt links combined with I/O stalls resulting from the inability of the PCIe lane adapters to keep a 40 Gbit/s channel full short of stuffing it with dummy packets.
Also, the total number of bytes being transmitted over the Thunderbolt link is slightly higher, as each tunneled PCIe packet includes an additional 4 byte header.
repoman27 - Tuesday, January 7, 2020 - linkThunderbolt 3 is 40 Gbit/s per link provided to the upper layers, full-stop. It doesn't care what protocol the packets are. The discrete controllers to date have only had at most a PCIe Gen3 x4 back end to the host. That is what limits PCIe bandwidth (along with a bit of additional overhead due to the Thunderbolt meta-protocol and channel-bonding). There are also up to 2x DisplayPort 1.4 sinks, which can be used by far more devices than the PCIe functions alone, especially on a controller with two 40 Gbit/s ports.
Thunderbolt signaling rates have nothing to do with the signaling rates of the PCIe back end.
Tiger Lake does have integrated Thunderbolt as well as PCIe Gen4 support, but usually Intel does not increment the Thunderbolt version number unless the front-end capabilities change. So this could mean USB 3.2 Gen 2 x 2 support and full USB4 certification.
quiksilvr - Tuesday, January 7, 2020 - linkSTOP IT. We have USB 4.0. Both in the consumer and enterprise world this has been an utter disaster. We have Dell D6000 USB-C docks that handle DUAL 4K60 monitors no problem on PC but refuse to work on Mac because it isn't Thunderbolt. Then we have the new Caldigit USB-C Pro Dock (which is also Thunderbolt 3) that works fine on Macs and PCs with 4 lanes PCIe but not PCs with a Thunderbolt port limited to 2 lane PCIe (even though those same computers work just fine with 10 Gbps on a USB-C dock). And the USB-C mode on the Caldigit dock only allows 4k60. This confusion branding nonsense was supposed to end with Thunderbolt 3 finally dying and we move on to USB 4. We don't need to bring Thunderbolt 4 back from the dead.
quiksilvr - Tuesday, January 7, 2020 - linkAnd the USB-C mode on the Caldigit dock only allows 4k60 on a SINGLE monitor, not dual.
lilkwarrior - Tuesday, January 7, 2020 - linkThunderbolt 3 is not dead; it's inclusion w/ USB4 IS what makes USB4 interesting + its side-effect of making it royalty free. It brings features USB simply does not have like daisy chaining.
Thunderbolt 4 is much needed since the core features of Thunderbolt are in need of a speed upgrade that many pros + Apple will strongly appreciate.