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

TidBITS Talk
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“Standards are great! There are so many to choose from.” anon

This article is the result of my quest to future-proof a purchase of a Thunderbolt/USB hub. I thought I’d pass on this information.

I wanted to see If I can connect my MBPr (late 2013) to a hub with a single cable. My MBP has these ports - 2 USB 3.0, 2 Thunderbolt 1 and 2, a headphone jack, HDMI, and MagSafe.

Note[ This is my 3rd crack are writing this article. The deeper into the rabbit hole I went (see title). the less clarity there was about which came first. Exploring that hole and a 5-week Covid experience leads to today. (I cannot recommend Covid to anyone, especially at age 79. I’m now vertical and trying to regain 22 lbs but I do feel great. Mask up.]

Starting with USB4 and Thunderbolt Announcements.
USB

  • introduces the Type C adapter as the logical follow-on to Types A and B.
  • USB4 deprecates all Type A and Type B connectors.
  • USB4 announces using the Thunderbolt Spec 3 for their next high-speed standard in pursuit of a higher transfer rate.
    Intel
  • announces Thunderbolt (in collaboration with Apple). Intel analyzed types of data transfers and concluded there were only two types - high-speed transfers of video/audio via Display Port, and memory/storage via PCIe. These are well-established standards already in use in Apple and PC devices.
  • the adoption of the Type C connector.
  • Thunderbolt 4 was announced in early 2020.
  • Apple is the first computer manufacturer to jettison the use of all USB connectors but Type C (for some MacBooks so far).
  • in June 2013 introduced Thunderbolt implementations of specs for 1 and 2 with USB Gen 3.1 and Gen 3.2 respectively.
  • This support page, Identify the ports on your Mac - Apple Support shows the Thunderbolt and USB connectors for various Apple computers. Note: these pages point out the differences between the Mini-DisplayPort connector for Thunderbolt 1 and 2 and older Mini-DisplayPort connections for video. These differences are:
  • for Thunderbolt the lightning bolt symbol appears on both the chassis port and male cable plug cover and has a white block inside the connector.
  • for the original Mini-DisplayPort connector, the old symbol is in both places and has no white insert.

Resources
USB4 USB history of protocols
USB4 usb.org spec

Thunderbolt
Thunderbolt 4 Wiki
Thunderbolt 4 Intel early details
Thunderbolt 4 Intel final details 07/08/20

SuperSpeed Wiki

Display Port Wiki

Direct Memory Access Wiki
Direct Memory Access Intel
Direct Memory Access Apple

PCie Wiki
PCIe Tom’s Hardware

Benefits to the computer manufacturers:

  • elimination of some device cards
  • elimination of continual change to the laptop chassis (carving holes) due to Type A and Type B changes.
  • elimination of the balancing of the mix and match of Type A and Type B connectors. These mixes never seemed to satisfy all users.

Benefits to Intel

  • Intel revenues are down with Apple’s departure and the race to the bottom of low-cost netbooks and laptops.
  • Apple’s collaboration with Intel on Thunderbolt provides a path to large-scale display setups and to mass data storage devices up to 3,500 Gbps.
  • USB4’s collaboration with Intel provides access to high-end (4K, 5k, 8K) video demands.

Benefits accrue to the Hub manufacturers:

  • more sales obviously
  • but, the mix and match of ports and various hub configurations will now be moved to the hubs at a cost to the end-users.

Benefit to end-users

  • provides a hub with a single power source and up to four Type C ports, and hopefully some future-proof improvements to new adapters. Hopefully.

Connections
Moving on to the cable between the two Type C connectors, first, look at the pin-out diagrams in the respective Wiki pages - Thunderbolt shows the use of 20 pins, and USB4 24 pins. Search for Google Images of these connectors, you’ll see what looks like a double-deck bridge. There are 4 high-speed lanes on each side and some low-speed lanes, and other sundry pins for control, power, and ground. End to end there are 11 pieces-parts - a 24-lane cable in the middle, two Type C adapters and 2 connectors, a pair of chips for each side of the Type C adapter, and computer/hub OS data processing senders/receivers reading and feeding each chip. Thunderbolt cables are short (.5 to 3-4 meters), can be passive or active connectors, and are expensive.

The Hubs
** As of 2/5/21 I have found announcement dates made in early 2020 for USB4 and Thunderbolt 4 but could find no release dates for either. However, rollouts are beginning now.
My take on this is that the USB4 and Thunderbolt 4 merged releases have agreed on pin usage and are aligned so they play nicely together. The third USB link above is from July 2020 and further describes the USB4 requirements of certification, direct memory access, data, and video speed, number of ports, charging, and wake-up. Apple M1 is not certifiable.

Wrap-up on my Quest

Well, my quest for the perfect hub is not in sight but the above OWC and CalDigit models might last for one or two computer upgrades.

My perfect hub would be a powered brick that contains nothing but Type C ports and a power source of some high wattage. The peripherals would connect to Type C male adapters (aka, use short dongles), e.g. a Lightning cable to Type C. When you order the hub, you would also order a small handful of dongles to suit your needs, connect them up to other peripherals, and put them anywhere in the brick. That would be future-proof.

But alas, this is not to be. But the OWC hub is looking good. But at $249.00. Maybe. I’ll have to see how this stacks up with the competition.

CES 2021: OWC Introduces Thunderbolt 4 Dock, New Storage Drives, and More

CalDigit’s Latest Dock Features Four Thunderbolt 4 Ports and Four USB-A Ports

My Solution

  • I do know the charging capability for my MBP cannot be used. But the hub is future-ready.
  • My USB Type-A connectors should be plugged into any USB port because USB is backward compatible with USB 2.0.
    = My audio connector is good as is.
  • My Thunderbolt 1 and 2 are convertible using new cable adapters, e.g. there is a Thunderbolt MiniDisplay to Type C cable available.
    I‘m not clear as to the HDMI port. If can be shunted over Thunderbolt, there is a Type C adapter that converts to HDMI at the monitor.
  • On the System Information page, you may see the Thunderbolt 1 10Gbps and Thunderbolt 2 20Gbps implementation. What’s not shown is the underlying USB Gen 2 (10 Gbps) and Gen 2x2 (20 Gbps) added to these protocols. I deduce this because my G-Drive external drive uses USB Gen 3.1 and this always shows as a Thunderbolt 10 Gbps connection even when the Mini cables were swapped.

Wrapping up this article
I hope the above helps with understanding the alpha/numeric soup, performance gains made over time, and some things about Thunderbolt and USB. Digging into the links above, you’ll find the manufacturers who make up the consortia for the various specifications, more about the history timelines, and much more detail.

My background covers 53 years of computer technology. This began with end-user/computer system programming/management and ended as a senior technical consultant to large and small companies and third-party developers to build high-performance, fault-tolerant programs with SQL databases and various communication protocols.

Hope this helps. Please contact me for questions, corrections, or comments.

regards, Mike Noonan

2 Likes
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Wow. A lot of this would have been quite useful when I was choosing a dock last month.

I think I know the ones you mean, Mike, but don’t find them “above,” am I missing something? In the end I went with a TB3 CalDigit unit for my new port-starved M1 Mini, and like it a lot. One of my considerations was the location of the “host” port–a front connection is fine for a laptop, but inconvenient for a desktop.

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Amazing info and yes my head hurts! I bought a dock for my 2015 MBPr in early December. I ended up with a Wavlink simply because I couldn’t swing the extra $$ for OWC or CalDigit after also buying a hard drive upgrade for the same machine.

My comments are: it was not so easy to find something that didn’t require USB-C as an input, or a more recent OS than Sierra.

My requirements were ethernet and USB port accessibility. I was unable to get the monitor working well through the dock so that is still plugged into the laptop.

One thing I read in some obscure place about a week after I set it up, was that while it works in Sierra, it may not in a newer OS (Mojave maybe). I found this odd considering the dock was introduced less than a year ago but haven’t had time to look into it fully yet.

Thanks for the research, it is really overwhelming at times!
Diane

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This just in from Caldigit may be what Mike wants: https://www.caldigit.com/thunderbolt-4-element-hub/. $180, pre-orders @ $140 direct.

Sorta solves my host-port-location gripe, and if I ever need another TB hub, my M1 Mini still has a port free . . .

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That’s a fine hub if your primary concern is more TB/USB-A ports. But note it doesn’t charge 16" MBPs at higher wattage (MBA and 13" MBP are fine though) and it has no other ports.

CalDigit also offers high-power charging along with a whole lot of other ports for $20 more, but of course with this one you only get half the USB-A (note only Gen 1) and USB-C (note not TB3!) ports of their Element hub.

https://www.caldigit.com/usb-c-pro-dock/

Both are particularly good at one thing, but not the other. It’s important people understand each one’s limitations.

Personally, if I’m spending that kind of money though I’d prefer getting one more TB3 downstream port and more type A ports (again only Gen 1 though). CalDigit has that for $250.

https://www.caldigit.com/ts3-plus/

But once you’re at that price point, you might as well get this OWC dock. Same price but more TB4 downstream ports and real Gen2 USB-A ports. Note no DP or HDMI ports (but you can use a dongle/cable off one of the TB3 ports for that).

But just to come full circle, the CalDigit Element compares really well to that, especially at the $140 introductory price. With the OWC TB4 dock you’re essentially paying over an extra hundred bucks for some added wattage, a Gigabit port, a card reader slot, and audio. Unless you absolutely need some of that (and note that apart from wattage all of that can be achieved with the appropriate dongle), chances are you’re better off with the Element.

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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.

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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.

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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.

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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.

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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?

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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:

1400×831 112 KB

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.

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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.

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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.

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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.

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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.

https://www.amazon.com/Cable-Matters-107022-Computer-Cables/dp/B084Z65YJQ

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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?

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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:

TB3 and USB-C cable standards
TB3 and USB-C cable standards1920×1270 137 KB

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