Thunderbolt, USB4, DisplayPort, PCIe, etc, Oh my!

Excellent points, Simon. I own the TB3, and chose it because it’s smaller than OWC’s & can be oriented vertically, and because its host port is in the back (see my comments above). It’s perfect for me.

I definitely get that. Never liked the host port on the front myself.

Personally, I’ve always been a fan of the TS3 Plus, but its age has started to show. I need Gigabit and DP so if I get an Element and throw in two dongles, I still saved $70 compared to the TS3 Plus and come out with more TB4 and Gen2 ports. At this point I’d only have reservations if I had a 16" MBP and needed full charging wattage.

OWC support said they’d moved it to the front because they’d had numerous requests for that from laptop users (that’s apparently what the market for docks is, mostly). CalDigit’s new one splits the difference by putting it on the side.

I heard that too, but I honestly don’t get it. I use my docks with MBPs and I never connect at the dock. I have the cable from my dock lying somewhere on my desk and connect that end to the MBP. The only port I’d want to see on the front is perhaps USB-A for connecting an iPhone or memory stick usage, rare these days though. Oh well, to each their own I guess.

And just for sake of completeness, Sonnet just released a new TB4 dock for $250, intro $200. This is essentially the same as the OWC, but at its introductory price it’s $50 cheaper.

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So can anyone tell why OWC’s new “one cable to rule them all” is better than the standard Apple Thunderbolt 3 cable?

Well, it costs less than Apple’s cable ($28 vs. Apple’s $39 for a 0.8m cable). Otherwise, the specs appear to be identical.

OWC’s own description of Thunderbolt 4: Intel Introduces Thunderbolt 4: What It Is and Does It Matter? includes the following infographic:

Look at the columns comparing Thunderbolt 3 and 4 and you’ll see that none of the differences should have any impact on cable construction:

  • Accessories with four Thunderbolt ports
  • Support for two 4K displays (only one was required by TB3)
  • 32 Gb/s of PCIe bandwidth (vs 16 Gb/s for TB3). But note that the overall bandwidth is still 40 Gb/s. The only difference here is the percentage of that bandwidth that may be used for PCIe data.
  • Required PC charging on at least one computer port
  • Required PC wake from sleep when connecting to a dock
  • Required Intel VT-d based DMA protection

It’s great that OWC is selling a cable that is certified for all applications (40 Gb/s Thunderbolt data, 10 Gb/s USB data, 100W power delivery), but these are all features that a “one cable to rule them all” Thunderbolt 3 cable should also have.

In other words, the “4” part of the cable’s description is completely superfluous, but it still looks like a good cable for a reasonable price.

That was my takeaway too, but I wanted to make sure. We’ll see if they reply to my question on their blog post about that with anything else.

The important difference is for cables beyond 80 cm. Beyond that length you need ‘active’ cables and at that point previous cables were either TB3-compatible or USB-C Gen2 compatible but never both due to the traditional retimer/redriver chips only supporting specific protocols (e.g. TB signaling rates). New “TB4” cables can be active for both TB3 and Gen2 protocols at the same time since they support all of the various signaling rates (DP alt, TB3, USB4, and 3 Gen1&2). So for >0.8 m where you need active there’s a crucial difference. Below you’re fine passive and then the whole issue becomes moot.

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Ah, interesting! OWC does say that “additional lengths are coming soon.” So perhaps that will be the point where the product becomes more compelling.

Thanks for that important point.

But it also underscores my point - that TB4’s big deal is that it is mandating features that were previously optional, but is not actually defining new features.

Of course, in this case, I don’t think anybody ever made an active cable supporting the full suite of optional protocols, which does make a “TB4 certified” active cable a big deal.

Good thing along with OWC, CalDigit today also announced TB4 cables but this time up to 2 m. It’s $80.

http://shop.caldigit.com/us/Adapters%20and%20Cables/Cables?product_id=207

Better yet, Cable Matters offers the same thing but at $58.

Soooo . . . that means that my CalDigit TS3+, which comes with a .7m TB3 cable and can provide, simultaneously, up to 13 USB, DisplayPort, ethernet etc. connections plus a TB3 pass-through to a TB3-equipped computer is, in effect, creating an active “TB4” connection to it. But would it require a TB4 cable and/or TB4 computer for a >.8m length? Or are both irrelevant upstream of the dock?

I think the simplest way of putting it it this. If you’re below 80 cm you can go “passive” and any cable should be fine. If you’re above 80 cm you need active. On an active cable, if you want to use it with both USB4 and TB3 and/or DP alt mode, it needs to be “TB4”. In your case, @David_L, you’re running this cable from a TB3 Mac to a TB3 dock so all that cable needs to do is TB3 and therefore you’re fine using whatever TB3 cable you fancy. BTW, the active/passive distinction relates to the cable, not the dock, the host, or the protocol across. Those all remain the same.

I think in general we should probably just start thinking of TB4 as being what TB3 should have been all along. TB4 makes sure we can use all our TB3 stuff (on the TB side from an end user perspective apart from multi-ports vs. daisy chaining nothing really changes) with all our USB-C Gen2 stuff using the same cables and docks and ensuring that either falls back gracefully to the other when required (within limits of course, i.e. pure USB4 cannot just magically become TB3). Of course it’s not helping with the confusion that Apple had to use the kludgy TB/USB4 (for established reasons) instead of ensuring full compliance with TB4 and just call it a day.

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Maybe this chart (TBH I forgot where I grabbed this from) will help clear up the point. It’s slightly outdated (doesn’t mention “TB4” or include USB4, i.e. things like USB 3.2 or DP 1.4 tunneling), but it does show what kind of a zoo is now being covered by the same cable, docks, and protocols through one unified TB4 standard. You can see how previously you really had to make sure what you got covers specifically what you’re trying to do. Now there is one TB4 cable/dock to rule them all. :+1: :slight_smile:

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O excellent, thanks, Simon. I’m assuming that the TB3 20Gbps options represent situations where the port the cable’s connected to shares a 40 Gbps bus–something that, as OWC notes, is true of Intel Macs but not of the M1 Macs released so far, where each port is a full 40Gbps.

I don’t think I will ever need to move my TS3+ further away from my M1 Mini than .7m, but am going to check the CalDigit website to see if they note any restrictions on cable length if you’re connecting to a 40Gbps port. Seems like they should. And I guess it may be possible to use a TB4 cable if you go >.8m.

For TB3 I think the 20 Gbps vs. 40 Gbps relates to how much PCIe bandwidth TB is left with. If besides TB you’re also running DP alt mode or USB across that pipe you need to set bandwidth aside for that so then only 20 Gbps is left for TB (and in fact that’s a simplification).

Note the minimum required PCIe bandwidth changed between TB3 and TB4 and presumably for exactly that reason. They want to ensure on TB4 that even when running a display and some USB peripherals off for example a TB hub, you’re still left with ample PCIe bandwidth for “TB” devices connected to that same hub. That spec called for the new retimer/redriver chips in longer cables since the cable itself is still max 40 Gbps, unchanged since 2015.

Why the M1s so far are all 40 Gbps/TB port I guess, and have (only?) two. Not something generally discussed, thanks, Simon.

I was aware of the connection limitations of my new M1 Mini compared to my old 2012 Mini (Firewire!) and factored a dock into the cost. It’ll be interesting to see if the next round of M1 Macs have more TB4 and/or additional USB C and A ports. If not, everyone will be buying docks and loudly sharing their pain.

I also found that to connect my M1 macMini to the LG 5K monitor I needed a Thunderbolt 3 5A cable. A plain Thunderbolt 3 cable resulted in intermittent screen artefacts and an annoying whine from the display electronics. I wonder if a USB4 cable/Thunderbolt 4 cable works in this situation?

OWC says their cable is functionally identical to Apple’s cable, though it’s obviously less expensive.

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