What you need to know about USB-C and Thunderbolt 3
By Paul Teich, Principal Analyst
I have a new Dell XPS 13 laptop with a Thunderbolt 3 capable USB-C port (I’ll explain the difference below). Here’s what I found out about USB-C and Thunderbolt 3 as replacements for previous generations of USB, video, docking stations, and future applications for tethered virtual reality (VR) and augmented reality (AR) headsets.
USB Type C, shortened to USB-C, is the newest USB connector and wire specification for everything from desktop PCs to smartphones. However, it is so new that not many consumers or manufacturers understand its full potential yet.
There are three key improvements in USB-C over previous USB standards:
- First and most visibly, USB-C uses one small double-sided connector spanning mobile devices to PCs, meaning that there is no upside-down or right-side-up way to insert the connector. Either way works, and it works the same for all devices! This is a big convenience boost from previous generations of USB, which could take a number of tries to get inserted right.
- USB-C’s power delivery spec enables consumer electronics companies to design desktop or entertainment system docks that can recharge a wide range of gear using one standard connector, from smartphones to laptops. However, there are important differences in the power ratings for USB-C wires, and consumers are not yet educated to look for those differences.
- USB-C keeps USB 3.1 data rates, at least for this first generation of USB-C products. But this is where dock and cable branding and specs are confusing, because Thunderbolt 3 uses completely different branding than USB-C and offers 4x higher data rates (up to 40 Gbps), but uses USB-C’s connectors. But where Thunderbolt 3 cables will work with USB-C devices, stock USB-C cables cannot support Thunderbolt 3 features and bandwidth.
Power Delivery is Not Standardized Yet
USB-C gives device vendors the option to supply up to 20 amps (A) of 5-volt (V) power delivery, which is up to 100 watts (W), over the cable, making it capable of recharging many of today’s PC laptops. The devil is in the details here, because not all USB-C cables will be capable of supporting high power delivery and consumers simply don’t have the engineering background to understand that the two cables pictured below may not do the same thing.
The two cables in the photograph above are not labeled consistently, don’t contain the same information, and neither specifies the wattage (important because the devices being charged don’t specify the necessary voltage and amperage requirements). One supports 9W and the other supports 25W, which is obscured by data. And, although “input” and “output” are meaningless for these cables, consumers might think there is a difference. But the really important point here is that neither of these cables should be used to push over 25W to laptops. By comparison, my XPS13 takes 65W to recharge. I would not want to use a 9W or 25W cable to do so.
The USB Implementers Forum’s (USB-IF) recently announced “Certified USB Charger” logo and compliance program to clearly mark chargers and stand-alone cables might help here. The USB-IF also announced the Power Delivery (PD) 2.0 v1.2 spec back in March, and those new features will roll into the upcoming PD 3.0 spec in the future. The PD 2.0 v1.2 and subsequent specs consolidate voltage and amperage ranges down to only five general power profiles:
- Up to 15W: this borrows from legacy USB specs and delivers up to 3A at 5V
- Up to 27W: up to 3A at 9V
- Up to 45W: up to 3A at 15V
- Up to 60W: up to 3A at 20V
- Up to 100W: up to 5A at 20V
We’ll see how the Certified USB Charger logo and cable label ratings are communicated to consumers by manufacturers. However, the sooner this is implemented, the better…especially because vendor specific alternate power delivery modes allow PC manufacturers to exceed 100W, which further complicates communicating power delivery to consumers. For example, Dell sells a USB-C dock that will supply 130W to its XPS15 laptop — that is possible because the dock, cable and laptop are all specified and designed by Dell. This somewhat bypasses the primary value of USB — providing a common standard. It may also be why some PC OEMs have not implemented USB-C yet.
High Speed Data is Relative When it is Shared with Video
USB-C has four high-speed data lanes, just like earlier USB 3 standards, and they operate at USB 3.1 speeds, so a USB-C cable has the same maximum data rate as USB 3.1–10 gigabits per second (Gbps).
USB-C also uses DisplayPort as its native video protocol. The 10 Gbps maximum data rate will support two 1080 HD monitors (1080p60 with 8-bit color resolution uses 4.46 Gbps per monitor), but doesn’t have the bandwidth to support 4K monitors. Whatever bandwidth is not being used to carry DisplayPort video data can then be used for other data.
Thunderbolt 3 is a separate cabling standard that layers on top of the USB-C connector and cable wiring; it is completely backward compatible with USB-C. Thunderbolt 3 creates two 20 Gbps connections using the same connector, for a 40 Gbps aggregate data rate — four times the speed of USB 3.1. 40 Gbps can support two DisplayPort 1.2 video streams with about 7 Gbps bandwidth left over (some of that is management overhead, so actual data rates will be somewhat less). However, 7 Gbps is much faster than stock USB-C data bandwidth with only one 1080 HD monitor attached.
Adapters for both USB-C to DisplayPort and Thunderbolt 3 to DisplayPort are very simple and inexpensive to build. On the other hand, HDMI and other video conversions are more complex to implement, requiring dedicated processor chips to actively convert data formats. As a result, USB-C and Thunderbolt 3 cables that support HDMI displays have a processor module in the middle and are more expensive.
The Thunderbolt family of technologies are Intel developed technologies; companies wishing to develop products based on Thunderbolt 3 must submit an application to Intel. Intel describes their Thunderbolt 3 license as a royalty-free, USB-like licensing model that is available to any company wanting to build a Thunderbolt 3 compatible product. Intel says it imposes no restrictions on the kinds of products a licensee might use Thunderbolt 3 technology; companies such as Lenovo or Samsung might design Thunderbolt 3 into both PCs and into their ARM-based smartphones. Intel claims that nearly 400 companies have signed a Thunderbolt 3 license. This bodes well for the future of Thunderbolt 3 outside of Intel’s core PC markets.
The HDMI Consortium further muddied the waters on USB-C cable types recently by announcing the HDMI alternate mode for USB-C. This alternate mode enables the host controller on a device — a smartphone, laptop, etc. — to commandeer many of the signal pins in the USB-C connector and cable so that a converter processor chip is not needed to support an HDMI connector on the other side of the cable. However, this specification will not allow other data to be transmitted simultaneously. The cable may be less expensive, but it will only be an HDMI video cable.
My Docking Solution
I implemented a three-wire docking solution for my XPS 13:
- Thunderbolt 3 dual-HDMI video converter: I’m only using one display at the moment, but I’m planning ahead. It’s the silver box at the top left of the photo below. I paid $100 for it via Amazon Prime.
- USB 3.0 7-port hub: Connects all of my USB peripherals with a dedicated 10Gbps of bandwidth, including an HD webcam, local storage and my gigabit Ethernet dongle (I like to reuse equipment, when I can). It’s the black box at the top right of the photo below. A new one costs $30 via Amazon Prime.
- Power.
Thunderbolt 3 desktop docks are still hard to find and expensive. I decided that for my first step into USB-C I would keep my legacy USB peripherals on a separate cable from my Dell 4K 34-inch curved monitor. I edit lots of high resolution photos and occasionally view/edit high resolution video. I’m not ready just yet to trust USB-C or Thunderbolt 3 bandwidth and data traffic management with all of the data going into and out of my laptop.
If I decide to buy a Thunderbolt 3 dock in the future, I’ll take my dual-HDMI video converter on the road to give me sharper presentations on higher resolution monitors.
Commentary
I don’t expect USB-C to displace HDMI or DisplayPort on desktop PCs. HDMI and DisplayPort are very well entrenched in the monitor and laptop supply chain and provide the highest video performance possible. Plus, USB-C will always follow the DisplayPort spec, not lead. For best performance, vendors will keep dedicated video ports on their desktop PCs.
However, USB-C will enable slim form factor PCs, tablets and smartphones to use standard PC and TV HDMI and DisplayPort displays without using bulky legacy video ports. That’s a big deal for all of those thin mobile form factors. Given that Microsoft Office runs on iOS and Android, and so does Adobe’s Acrobat Reader, I can see a future where smaller mobile devices with HDMI dongles can drive conference room displays. USB-C will also make it possible to edit documents using a mobile device with a desktop dock and to drive a presentation from those mobile devices when roaming.
Over the next year or two, USB-C seems perfect for laptop and tablet PC travel docks. I do have a Dell USB-C to HDMI/VGA/Ethernet/USB 3.0 dongle (model DA200) for presenting to customers and at events. It replaces three separate dongles I have been carrying: a USB 3.0 gigabit Ethernet port, a mini-DisplayPort (mDP) to VGA video converter and a mDP to HDMI, DVI, and full DisplayPort video converter. I bought that last one for flexibility, but I have never seen a DVI or DisplayPort connection at a conference or customer site. It’s all HDMI and legacy VGA.
But here lies the first challenge for USB-C as a “do everything” connector — video and high-speed data use the same four signaling lanes. This should not be a challenge if you have only one 1080p monitor attached to a USB-C port. In this situation there should be plenty of USB-C bandwidth to support network connections and light external storage drive use.
If, however, you are a power user with more than one 1080p HD monitor or are using a 2K or higher monitor, then your high-speed video bandwidth will crowd out your high-speed storage drives and gigabit networking. Thunderbolt 3 cables are a great alternative, but only if the device supports it (not many do today and Thunderbolt 3 docks are still hard to find and expensive). Consumers will also have to be educated to look for the Thunderbolt 3 brand and not stock USB-C cables.
For road warriors, a more pressing question is — what about wireless docks? I saw a few WiGig docks at last January’s Consumer Electronics Show (CES), but they don’t seem to have made a big dent in the market yet. The 60GHz WiGig spec supports a maximum 7Gbps data rate, which puts it in USB 3.0’s territory for only supporting a single HD display simultaneously with network, audio, and other device traffic. WiGig’s close range of one to 10 meters means that wiring individual room projection systems has little return on investment over simply using a wire to connect to a display in those rooms. Eventually it would be great to wirelessly dock a device while it wirelessly charges, but we’ll need much better bandwidth and range before that happens.
Power users might therefore opt for two or three wires in the near term. Power users typically attach multiple and/or very high resolution monitors to our PCs, and perhaps have USB 3.0 direct attached storage (DAS) and hard-wired Ethernet network connections.
As I looked into Thunderbolt 3, I began to see the perfect end-game for Intel and the PC market in promoting Thunderbolt 3 ports on laptops, tablets and smartphones — commodity consumer VR/AR headsets. Thunderbolt 3 supports two very high resolution displays, multichannel audio and has enough bandwidth to transmit real-time sensor data from a headset to a mobile device with very low latencies.
For at least the next few years, PC processors with integrated graphics with optional AMD and NVIDIA outboard graphics accelerators will support higher performance stereoscopic display systems than mobile graphics. Tethered VR/AR headsets can support higher resolution displays and a more tailored set of sensors than make sense on smartphones. Smartphone-based VR headsets are already powered by the smartphone battery, but Thunderbolt 3 based headsets would enable consumers to keep their smartphones pocketed, reducing the weight of the headset. Graphics power, user experience (UX) and battery life would be offloaded to whatever mobile device the headset is currently plugged into — from smartphone to desktop PC.
Thunderbolt 3 ports are available on gaming laptops from Dell’s new Alienware laptops, which include separate NVIDIA GeForce series graphics chips that can support VR performance and display resolutions. MSI has also recently introduced a gaming laptop with an NVIDIA GeForce graphics chip and Thunderbolt 3. AMD also requires Thunderbolt 3 to be implemented at a system level for their customers who implement AMD’s XConnect technology. XConnect enables laptops with Radeon R9 series GPUs to connect external full-sized Radeon graphics cards using a Thunderbolt 3 cable.
Intel’s Thunderbolt 3 presentation at Computex in June says “expect Thunderbolt 3 to drive next-generation VR solutions with high resolution and refresh rate, and low latency.” We can’t see any yet, but we will continue to monitor the VR headset market for Thunderbolt 3 enabled product.
I like the direction that USB-C is heading, but it’s not yet a complete solution for high-end laptop and tablet PC owners. I very much look forward to the second generation of USB-C and Thunderbolt 3 connectors giving all PC owners a vendor-independent single-wire dock in a few years. And I’m really looking forward to competition in VR/AR headsets, and maybe even a few open hardware choices!
— Disclaimer: We are not a testing lab — we occasionally evaluate products by using them in our high tech road warrior lifestyles. Dell sent me demo units to evaluate.
