Published on 17th July, 2019 by Cable Chick

The Complete Guide to Thunderbolt & USB-C

The Complete Guide to Thunderbolt & USB-C

Thunderbolt® is an impressive technology, but it can be hard to fully understand. Read our blog on Thunderbolt, Mini-DisplayPort, and USB-C to learn how they all work.

Understanding Thunderbolt

In and of itself, the Thunderbolt interface is very straightforward, offering a wide variety of high-speed data lines for use with a number of different devices and accessories (more on them later). The real confusion sets in because Thunderbolt has always shared its connector with another, pre-existing technology, leading to miss-identification and incompatibilities.

In this blog, we separate Thunderbolt from its connector type, explain what it can do, and try our best to make the convoluted mess a bit easier to understand so your future tech purchases live up to your expectations. This blog is focused on mainstream consumer usage, so specialised edge-cases may be overlooked for the sake of clarity.

Thunderbolt 3 offers more of everything


We use a few technical terms in this blog, and we thought we'd explain them all here so you don't get lost.

Host or Host Device

A host device is the computer that controls connected peripherals. Usually this is your laptop or computer

Alternate Mode

Alternate Modes are special features of USB or Thunderbolt which are optionally supported by the manufacturer. A USB-C device may support video output using the DisplayPort Alternate Mode

Passive Cable

An all-copper cable that only contains standard controller circuits. Typically these are limited in length but not in compatibility

Active Cable

Active cables include a special chip which can boost the length of a cable by using extra power to overcome resistance. These cables are typically longer than passive options, but may not support high charging rates or all Alternate Modes

DP or Mini-DP

Just a shorter way of writing DisplayPort

Thunderbolt & Mini-DisplayPort (2011 to 2018)

For the first two iterations of Thunderbolt, Intel™ and Apple™ joined forces and leveraged the Mini-DisplayPort socket, meaning some devices with a Mini-DisplayPort socket were Thunderbolt-enabled, and some weren't. They key identifier was the logo on devices and cables. Mini-DisplayPort had the box icon or DP icon (or no icon) and Thunderbolt had, well, a lightning bolt.

Mini-DisplayPort and Thunderbolt Sockets
Left to Right: Mini-DisplayPort Socket, Thunderbolt Socket, Mini-DisplayPort Socket

Mini-DisplayPort connections and cables are only used for computer monitors. Much like HDMI, DisplayPort and Mini-DisplayPort carry video and audio, plus some other related data, to a display. These links are typically limited to 17.28 Gbit/s (known as HBR2) and offer 1080p@120Hz or 4K@60Hz. Mini-DisplayPort was ubiquitous on the Apple Mac, iMac and Macbook ecosystem, but also found use on Windows-based desktop and laptop computers.

Thunderbolt 1 and Thunderbolt 2 used the Mini-DisplayPort socket, but worked a bit differently. As well as providing a DisplayPort video link, they included PCIe protocol support for accessories and peripherals like FireWire dongles, storage devices and LAN connectivity. The purpose was to make a single connection on your PC or Laptop dock with all your peripherals. You could run two 1080p monitors, an external hard drive and your wired internet connection through a single socket, then unplug just one cable to take your laptop away.

Theoretically, you could use Thunderbolt's bandwidth any way you liked, either on a single high-resolution, high-refresh-rate display, or on a smaller display together with several peripherals. Thunderbolt 1 supported DisplayPort v1.1a at 10Gbit/s, while Thunderbolt 2 was upgraded to DisplayPort v1.2 at 20Gbit/s without changing the cables.

Mini-DisplayPort Cable vs Thunderbolt Cable
Left to Right: Mini-DisplayPort Cable, Thunderbolt Cable

Thunderbolt and Mini-DisplayPort cables have always been separate beasts. Thunderbolt features absolutely require Thunderbolt cables (and devices) at every step. For video-only, a Mini-DisplayPort cable can also work in a Thunderbolt socket, but won't carry the PCIe protocol data.

Thunderbolt 3 and USB-C (2018 - onwards)

Thunderbolt 3

Now that 4K is mainstream and we're transferring more data than ever before, Intel have updated Thunderbolt to provide extra speed and functionality, but this time they're using the USB Type-C connector. This is super-confusing as Thunderbolt and USB have a lot of overlap in functionality. Again, only Thunderbolt 3 cables will support all Thunderbolt 3 features (including USB), while regular USB cables will only work for USB (and USB Alternate Modes where available).

Thunderbolt 3 offers a variety of Modes it can operate in, depending on the hardware manufacturer's choices and the cable that's attached:

  Thunderbolt 3 Alternate Modes

Thunderbolt 3 Mode

Full-featured Thunderbolt 3 at 20 or 40Gbps, usually with all the bells and whistles

USB Only

Works just like a USB 3.2 Gen 2 (or lower) connection for data transfer (no USB Alternate Modes!)

DisplayPort Only

Routes raw DisplayPort data (video and audio) from a graphics processor to a display up to 4K@60Hz

DP + USB Multi-Function

For data/display docks up to 2560x1600 QHD, plus USB 3 for data

Thunderbolt Networking 10GbE+

10Gb Ethernet connection between Thunderbolt 3 enabled computers

Power Delivery & Charging

Charging (the host) up to 100W, or sending power to other devices at up to 15W

You might imagine that all Thunderbolt 3 enabled hosts devices would support all of these features at their maximum specification, but in reality hardware manufacturers are free to save costs by only supporting the protocols and modes they need or want, and to any level they desire. For example, a Thunderbolt 3 device may only support 60W charging rather than 100W.

This flexibility comes at the cost of simplicity, as users must now dig into user manuals and specifications lists to find out what their devices are actually capable of. You won't be able to rely on the icons near the socket alone to state all its capabilities - there's just too many features for them to all fit. And neither will the fastest cable guarantee your hardware can keep up.

Thunderbolt 3 Cables

Thunderbolt 3 Cable
The "3" on this plug designates full 40Gbit/s compatibility.

Cabling for Thunderbolt 3 is relatively straight-forward. Thunderbolt 3 cables up to 50cm can be 40Gbit/s compatible and will do everything their host device supports. Copper-only 'passive' Thunderbolt 3 cables over 50cm are generally only 20Gbit/s compatible and that in turn lowers resolutions or slows down peripherals. Active Thunderbolt 3 cables (which cost much more than their copper-only counterparts) can retain 40Gbit/s over longer lengths, but some achieve this at the cost of Power Delivery - meaning they're no good (or not as good) for charging.

Thunderbolt 3 cables are ALWAYS USB-C to USB-C and are marked with the Thunderbolt logo and a "3" if they have 40Gbit/s support..

USB-C and USB 3.2 Gen2x2

The USB-IF has made understanding USB a bit of a joke at this stage. They've changed the naming conventions for USB 3.0 three times, with only mild changes to the underlying hardware and features. The key here is that USB Type-C (a.k.a. USB-C) will only ever refer to the connector (plug). USB-C is not a designator for speed or functional support.

USB 3.2 Gen 2x2 is the current highest specification for speed and functional support, and offers a variety of Alternate Modes it can operate in, depending on the hardware and the type of the cable.

  USB 3.2 Gen 2x2 Alternate Modes

USB 3.2 Gen 2x2

Data transfer at 5Gbit/s (cables under 2m), or up to 20Gbit/s (cables under 1m)

USB 3.2 Gen 1 or Gen 2

Data transfer at 5Gbit/s (Gen 1), or 10Gbit/s (Gen 2), or sometimes USB 2.0 speeds!

Power Delivery 3.0

Charging for devices at 5V, 9V, 15V, or 20V at any wattage between 0.5W and 100W

DisplayPort v1.4b

Video up to 5K@60Hz or 8K@30Hz

HDMI v1.4b

Video up to 4K@30Hz

HL and superMHL

Video up to 8K@60fps


Not yet standardised (intended for VR HMDs)

Similarly to Thunderbolt, but perhaps with room for even more confusion, there seems to be no limit to the variety of implementations manufacturers can opt for when building a device with a USB-C socket. According to specifications, a USB-C socket may support as little as USB 2.0 data speeds and power, or as much as everything in the list at full force. Or any combination in between.

USB Naming and Renaming

The USB 3.0 spec started at 5Gbit/s, but as it sped up to 10Gbit/s and then 20Gbit/s, it kept changing names and version numbers. These changes (listed below) are irrelevant to cables, and really only serve as identifiers for manufacturers of host devices like computer motherboards and laptops. These specifications (regardless of their name) are completely separated from the plug type. They can theoretically be Type-A, Type-B or Type-C and still support any of these speed profiles.

  USB 3.2's previous names

USB 3.2 Gen 1

5Gbit/s - Originally USB 3.0 and what we typically think of when we see a blue Type-A socket. Also changed to USB 3.1 Gen 1

USB 3.2 Gen 2

10Gbit/s - Originally USB 3.1, but quickly changed to USB 3.1 Gen 2

USB 3.2 Gen 2x2

20Gbit/s - Originally USB 3.2, but with the other renamings it had to stay special


Future USB specification with 40Gbit/s support

USB 3.2 Gen 2 Cables

USB 3.2 Gen 2 over USB Type-C Cable
The SS-10 icon states this cable is SuperSpeed 10Gbit/s compatible.

The flexibility of USB 3.2 makes it extremely difficult for consumers to know what their devices are capable of, and for retailers to recommend the right cable! Look for the SuperSpeed or the SS10 Trident icons to identify what speed a given cable is likely capable of, but also check the product description or packaging for information on Power Delivery and Alternate Mode support. Power Delivery is especially murky, with manufacturers able to pick and choose from a number of voltages and almost any wattage they desire.

Thunderbolt 3 Cable
Some of the icons you may see on USB host devices. The battery icons designate some level of Power Delivery support, and the DisplayPort logo shows Alternate-Mode support for video output (but not Thunderbolt!).

USB Type-C cables also come in additional flavours to support USB Alternate Modes, like a USB-C to DVI cable intended for use on a device with DisplayPort Alternate Mode Support, as well as more traditional USB Type C to USB Type-A cables for use with peripherals. Typically a Type-A connector will be 5Gbit/s, but manufacturers can make them go faster if they wish.

Cables Are Getting Shorter

Thunderbolt 3 supports all its features at only a half a metre, which is going to be a problem in most environments. Both Intel and USB (and HDMI and VESA in the near future) are claiming outrageous new transfer speeds but achieve them by making cables so short they become impractical to use. Long gone are the days of 20 metre HDMI cables and 5 metre full-speed USB cables. The USB 3.2 Gen 1/2 specification only allows for 1 metre cables to support 10Gbit/s. Any longer and you're back to 5Gbit/s. USB 3.2 Gen 2x2 at 20Gbit/s may be even shorter.

USB-C cables that do not have shielded SuperSpeed pairs, sideband use pins, or additional wires for power lines can have increased cable length, up to 4 m. But these USB-C cables only support 2.0 speeds and do not support Alternate Modes! That's a hefty cost to reach 1m less than a regular old USB 2.0 cable!

In the future, manufacturers may develop ways to make cables longer and still retain full functionality, but right now the longest cables are Active versions, which usually means sacrificing Power Delivery for data speed in both Thunderbolt 3 and USB 3.2 applications. Some Active cables are better than others, so it will come down to brand, price and those all-important manufacturer specifications.

Whether USB or Thunderbolt 3 - Always look for the logos on your cables and devices to ensure they both share the performance and compatibility you need.

The Bottom Line

Thunderbolt 1 and 2 devices are no longer being produced by Apple, and accessories which support it are likewise dwindling in favour of Thunderbolt 3. Older Thunderbolt devices, all the way down to FireWire dongles, are still supported via Thunderbolt 3 if you buy the right adapters or docks, but for all future tech the focus will be on USB-C with Thunderbolt 3 support at 40Gbit/s up to 50cm or 20Gbit/s for anything longer.

For consumers, that means looking for a cable which specifically states the requires transmission speed at the length you need, and being prepared to make a compromise as cables are getting very short indeed. For feature support, you'll have to dig into your user manuals to find out what your Thunderbolt 3 host device can accommodate. The good news is that there are really only two types of standard cable to buy: Short-but-fast ones, or long-but-slow ones.

USB 3.2 Gen 2x2 using USB-C at both ends will remain the top contender for full speed 20Gbit/s features outside of Thunderbolt 3. The alternate mode flexibility discussed above makes it very important to check those device specifications, but a Type-C to Type-C cable supporting SuperSpeed+ at up to 1m should do everything possible, but check its specs for Power Delivery rates.

For other USB implementations, such as USB-C to Type-A, the expectations fall sharply to SuperSpeed 10Gbit/s on select devices, or even 5Gbit/s everywhere else. Again, longer cables will have lower data and charging speeds, so always opt for the shortest cable you can live with and be prepared to discover your device isn't as fast as the cable. Most manufacturers happily label their Type-A sockets when they support 10Gbit/s, so keep a sharp eye.

USB 3.2 Gen 2 and Thunderbolt Together
Left to Right: USB 3.2 Gen 2 on USB-C, USB 3.2 Gen 2 on Type-A, USB 3.2 Gen 1 on Type-A, Thunderbolt 3 on USB-C, and USB 3.2 Gen 1 with Power Delivery on Type-A.

For USB-C to DisplayPort/HDMI/DVI/VGA video cables, you'll again have to check that your device supports that specific USB Alternate Mode. USB-C to Video cables are NOT Thunderbolt 3 compatible. Wikipedia keep a list of devices with video output over USB-C, but they don't say which protocol they're using. The assumption is DisplayPort, as it offers the most flexibility, but always check for the DP, HDMI or MHL icons in your user guides.

USB Video Output Modes
Only one of thse icons is likely to appear at a time next to a USB-C port


Feel free to contact us if we've missed any information or if you have further questions!


The SuperSpeed USB 10 Gbps Trident Logo, Trident Logo and USB Power Delivery Logo are registered trademarks of USB Implementers Forum, Inc.
DisplayPort and the DisplayPort logo are trademarks owned by the Video Electronics Standards Association (VESA®) in the U.S. and/or other countries
MHL, Mobile High-Definition Link and the MHL Logo are trademarks or registered trademarks of the MHL, LLC

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