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Comment by maxsilver | Hacker News Reader

> Needs to filter whether it can show HDMI 4K at 30Hz or 60Hz. And related to that, for video, it’s possible to have 2 4K 60hz through or one or none.

I don't think they'd bother, because none of these docks can do it. USB-C 3.1 inherently can't support a 4k@60hz display, due to bandwidth limitations. And it certainly can't run two of them.

You'd have to jump up to a Thunderbolt 3 dock for that sort of thing.

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The Thunderbolt capable docks on Amazon are still listed as USB-C because consumers seem to think it’s all about cable shape.

That said, there are plenty of dual USB-C connector, dual HDMI 4K@60hz port, dongles designed for Mac on Amazon. I think this is the most recent addition:

https://smile.amazon.com/gp/product/B07RH9HF4R/

”Satechi Aluminum Type-C Dual HDMI Adapter 4K 60Hz with USB-C PD Charging — Stunning dual HDMI display with a convenient USB-C PD port to keep your setup up and running - all in 4K 60Hz resolution. ENGINEERED FOR 4K DUAL DISPLAY - features dual HDMI ports to connect two monitors for stunning, extended 4K 60Hz display. Requires a direct HDMI connection, will not work with VGA, DVI or Thunderbolt displays...”

By contrast, this is one HDMI 4K@60Hz and one HDMI 4K@30Hz:

https://smile.amazon.com/Satechi-Multimedia-Adapter-Gigabit-...

Includes the two 4K HDMI ports of differing refresh rates, USB-C PD 3.0 charging, Gigabit Ethernet, micro/SD card readers, and USB 3.0 ports, and also will not work with Thunderbolt.

Two 4k @ 60 Hz is either Thunderbolt (which is fine for Macs but has a price and I would rather buy like https://www.monoprice.com/product?p_id=38575 or https://www.monoprice.com/product?p_id=31261 instead of a noname company) or DisplayLink which is to be avoided at all costs. This hub is Thunderbolt as can be deciphered from "Does not support MacBook models with single USB-C port" (see https://support.apple.com/en-us/HT201736#usbc ) but the fact I need to decipher what it is a second strike against it. It seems lately Intel has loosened its iron grip on Thunderbolt 3 (after all, it handed the standard over to USB IF) so now everything goes (we see empty M.2 to TB3 enclosures and chaining eGPU boxes both of which were forbidden by Intel prior) but the fact they didn't include the trademarked name makes me go hm.

Finally, it could be a DP 1.4 MST hub but that is very rare (the first USB C to DP 1.4 MST I am aware of was announced at CES 2020 https://plugable.com/2020/01/07/plugables-new-docking-statio... and didn't ship yet) and figuring out support will be _very_ interesting. All Intel 14nm laptop CPUs are stuck with DisplayPort 1.2 and then researching which laptops with Radeon / nVidia GPUs run their USB C through those GPUs to provide DP 1.4 will be fun.

Let's put 4k @ 60 (and then 4k @ 30) into the bandwidth calculator: https://linustechtips.com/main/topic/729232-guide-to-display... you can see you need more than what DP 1.2 can provide so everything I said above applies.

Oh and of course if it's for a Mac, in general, you could just use two USB C plugs, I suspect that's what the 4k @ 60 + 4k @ 30 is: one plug is used in DP alt mode, the other is used in MFDP mode.

It doesn’t support macs with a single port because it takes two ports, uses each one. That changes the bandwidth calculator math.

This adapter was, I believe, also announced at CES 2020.

Oh I see now https://images-na.ssl-images-amazon.com/images/I/71z-IlmfZeL... the single plug misled me to think it's just one USB C. Crafty.

Intel may have ostensibly handed the standard over to USB IF but all of the reference designs you'd use to implement a Thunderbolt dock are behind NDAs and unavailable [1] unless you get lucky, have an existing relationship, or have the volume to get their attention.

[1] https://thunderbolttechnology.net/developer-application

Yeah but it used to be that Intel needed to certify every TB3 device and they wouldn't certify a PCIe enclosure as eGPU if it chained. Neither they would an empty M.2 key M enclosure. Both now exist.

> or DisplayLink which is to be avoided at all costs

May I ask why, or is it the details you have later in your post?

DisplayLink transports video over the USB bus, rather than using one of the alt modes of USB-C. As you can imagine, this introduces compression artefacts and substantial CPU overhead. It's passable for web browsing. Watching any sort of video is painful and forget about any sort of gaming or latency sensitive application

Ah, this is why the displayport to 1080 screen connection looked so bad. I have a mediagear usb-c hub and also a cable matters thunderbolt to dual displayport adapter. Video is much better over the latter, for sure.

DisplayPort is fine.

DisplayLink is not.

The confusion is deliberate, the company renamed itself to DisplayLink a few months after the standard came out.

Sources: it was USB NIVO before the DisplayPort standard came out https://www.cambridgenetwork.co.uk/news/491654

and then

https://www.businesswire.com/news/home/20061106005769/en/New...

https://glenwing.github.io/docs/DP-1.0.pdf DisplayPort Standard Version 1 May 1, 2006

Thank you for replying to me multiple times with concise, clear, and informative comments. I really appreciate that.

Ahhh, thank you, that clears it up.

Sorry, to clarify, you technically can get enough bandwidth for 4k@60hz out of a USB-C port, but you have to abandon the data lanes for more DisplayPort lanes. (I.e, give up all of your USB 3.0 ports and gigabit ethernet or similar-speed ports). So, "adapters" can do it, but docks generally can't.

https://www.bigmessowires.com/2019/05/19/explaining-4k-60hz-... has the specific technical details.

Yes, that link was in my top level post. :-)

And that’s why I’m linking to adapters that use two of the Macbook Pro ports.

That‘s not generally true.

Apple‘s newer model multiport adapter does 4k60 and USB 3 on devices supporting DisplayPort 1.3 (which is required to fit 4k60 into two instead of four lanes).

That's the magic of displayport for you. It won't do that on HDMI, except with active converted from DP to HDMI :)

I'd assume that all of these hubs are using DisplayPort though?

HDMI alternate mode hasn't really caught on, especially since it uses all high-speed lanes on USB-C. This leaves no room for USB 3 ports on a combined hub.

> The Thunderbolt capable docks on Amazon are still listed as USB-C because consumers seem to think it’s all about cable shape.

Thunderbolt docks with Titan Ridge controllers fall back to USB capabilities/bandwidth if connected to a USB-C non-Thunderbolt host.

Satechi always sounds funny to French people. Pronouncing the name literally means in casual language "it poops you".

Never realized that until you mentioned it. And I've owned some of their products for a long time. I guess it's because I figured it was pronounced "satéchi" which is more likely sound for an Asian company ("saké" and not "sakeuh")

> consumers seem to think it’s all about cable shape.

As others have noted, the Thunderbolt/USB landscape is pretty confusing.

You can do 3840x2160@60Hz (and 24bpp/8bpc) over USB Type-C on newer displays. DisplayPort Alt Mode over USB-C using DisplayPort 1.3/1.4 can support 4K + USB 3 Gen2 on one cable.

https://www.amazon.com/UPTab-10Gbps-60hz-Power-Delivery/dp/B... is an example

Exactly.

Apple also recently quietly updated their multiport adapter to do just that:

https://support.apple.com/en-us/HT207806

Intel (GPU) Macs are notably not supported, unfortunately (due to supporting DisplayPort 1.2 only).

USB-C 2.0 can support 4K60 (see deep dive above) so you can drive one good monitor if you don't need fast network or storage.

did you mean USB-C at USB 2.0 speeds?

there is no standard by that name and Rev 2.0 does not mention video

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