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Device Connections Explained: Thunderbolt or Not, It’s All about USB-C

If you’re not sure of the differences between USB-C vs. Thunderbolt (3) or between USB 3.0 vs. USB 3.2, you’re not alone.

But mind you, we’ve been in a pretty good place for a couple of years now. Not so long ago, we had to also deal with a myriad of other peripheral connections types, like Parallel, Serial, FireWire, eSATA, and so on.

This post will help you understand the current state of modern connection standards — namely USB and Thunderbolt — so that you can plug one device into another with confidence.

There are two things to keep in mind in laymen’s terms: connection type and connection standard. Let’s start with the type.

Dong’s note: I first published this post on  November 13, 2019, and updated it on August 5, 2021, with additional up-to-date information.

The SanDisk Extreme Pro Portable SSD's USB-C port
The SanDisk Extreme Pro Portable SSD uses the USB-C connection type.

1. Connection type: How things fit

We generally use a cable to connect a device (like a portable drive) to a host (like a computer). This cable, like all cables, has two ends, which are male connectors or connectors for short.

One end goes into a host, and the other goes into the device itself. The holes the cable’s ends plug into are female ports or ports for short. The configuration of a port determines its type. Each port type has its corresponding connector.

USB-C port type is the new norm

Most modern devices use USB Type-C (or USB-C for short) port type.

In this case, both ends of the connecting cable are the same; they are USB-C connectors. It’s super convenient — you don’t need to figure out which end of the wire goes into the host and which is for the device.

The USB-C port also features reversible plug orientation, meaning you can plug the cable in with whichever side up or down.

What’s more, USB-C also works as the power connector for large devices, like a laptop — the machine won’t need a dedicated power port anymore — and it can deliver power both ways. So, for example, when connecting two smartphones using a USB-C cable, you can share data and power between them.

This convenience is available to the latest USB standard and Thunderbolt 3, which also uses USB-C port type.

(I’m aware of Thunderbolt 4, as you’ll note in the Connection Standard section below, but stay with me! You’ll understand why TB3 is more significant by the end of this section.)

In other words, when all of our devices support USB-C, which is the way of the future, there’s no need to worry about what cable to carry anymore since there’s just one type of cable.

Well, almost. Unfortunately, things are more complicated than that. For one, thunderbolt and USB are not fully compatible.

Samsung X Portable SSD Thundebolt 3 Cable
The Samsung X5 is a Thunderbolt 3 drive. Note its TB3 cable, which looks the same as a USB-C one.

Port types: Thunderbolt 3 vs. USB-C

All Thunderbolt 3 ports work as a USB-C port, but not vice versa. As a result, you can plug a USB-C portable drive into a TB3 port, and it will work as intended.

However, a TB3-only device, like the Samsung X5 portable drive, will not work when plugged into a USB-C port, even though its cable fits perfectly. The reason is TB3 has more requirements. There’s more to a TB3 connection than a USB-C-based USB one.

As for the connecting cable, all TB3 cables work as USB-C ones, but only high-quality USB-C cables can also work for TB3 — “low quality” ones might work but at a much slower speed or are just unreliable.

For this reason, a TB3 cable tends to come with the TB3 symbol, and that’s the only way one can visually distinguish one from a USB-C counterpart.

And then we still have to deal with other non-USB-C port types, too.

Legacy USB port types

Since there are billions of existing USB devices on the market, it’s essential to support them. And as a result, for the foreseeable future, chances are you’ll run into older USB port types.

In this case, remember that, now, the connecting cable has two different ends: A and B.

Synology DS USB Ports
The USB Type-A port is everywhere. Here are two of them behind this small NAS server.

USB Type-A

The end that goes into a host is called a USB Type-A connector.

Before USB-C, this connector and the corresponding port tye — the USB-A female port — remain the same in all USB standards.

There are two USB Type-A versions:

  • USB Type-A: Used in USB 1.1 to USB 2.0 and supports speeds up to 480 Mbps.
  • USB Type-A SuperSpeed: Used in USB 3.x standards — more on this below — and supports speeds up to 10Gbps. It tends to come in blue.
USB Type A 1
USB Type-A and Type-A SuperSpeed connectors. (Not to scale.)

Again, these two types use the same port and work interchangeably (at their speed). In other words, USB Type-A SuperSpeed is backward-compatible with USB Type-A.

If you start getting confused, well, it’ll get much worse.

USB Type-B

This type is the other end of the cable that goes into a device. This is where things get very complicated.

There are so many variations of standard USB Type-B. That’s not to mention the countless non-standard proprietary Type-B designs, of which the most famous is the Apple Lighting connector that goes into an iPhone.

Each variant of Type-B connectors requires a corresponding port of its own. Physically, one variant’s connector won’t fit into another’s port. As a result, each port type requires a distinctive cable.

So, for example, if you have an iPhone and another non-Apple device, you’ll have to carry at least two cables.

USB Type B Standards
A few variations of USB Type-B connectors. (Not to scale.)

Following are some, out of many, Type-B standards:

  • Standard-B (or Type-B): Used in USB 1.1 and USB 2.0 standards. It suits mostly large devices, like printers or scanners.
  • Standard-B SuperSpeed: Available only to USB 3.x devices, this port type also works best for large devices, like a desktop external drive.
  • Mini-USB (or Mini-B): Significantly smaller than Type-B, this standard is for old portable devices, such as clamshell phone, first-gen portable drives. It’s mostly obsolete now.
  • Micro-USB (or Micro-B): Slightly smaller than Mini-USB, this port was once the go-to type for older generations of smartphones and tablets. It’s also being phased out.
  • Micro-USB SuperSpeed: The thin version of the Standard-B SuperSpeed. It’s popular in portable hard drives, like the WD My Passport.

Again, as you can imagine, with so many port types, finding the correct cable for your device can be a pain in the rear, especially when you’re in a hurry. This problem is why the USB-C port type mentioned above is such a knight in shining armor.

Legacy Thunderbolt port type

Even though much younger and more “modern,” compared to USB, Thunderbolt has port issues, too.

That’s because, before Thunderbolt 3, there were Thunderbolt and Thunderbolt 2, which use the Mini-Display port type. This standard was one made exclusively for MAC with limited usage.

As a result, there aren’t many “legacy” Thunderbolt devices, and Thunderbolt 3, which is the first revision of the standard available outside of the Apple ecosystem, generally doesn’t support Thunderbolt 2 and Thunderbolt devices. Some can work via an adapter, but in most cases, they don’t work well.

That said, Thunderbolt 3 is the first TB revision that breaks away from the TB norm, which is the only reason why it can compete with USB.

And the fact it uses the USB-C port type means USB is too important to ignore. Future Thunderbolt revisions will also use the USB-C port type.

Final thoughts on USB-C connection type

Small, cute, and well designed, USB Type-C is a new port type aiming to replace all other USB port types, giving users one unifying port standard.

The fact Thunderbolt 3 also uses this port means, from now on, it will be the prominent type. So far, it’s the only USB port that can work all existing USB standards (except for the ancient USB 1.x), and chances are it will also support future connection standards.

See also  Gigabit Internet Explained: Understanding Magic of Those Gbps

By the way, all USB-C devices can connect to a USB Type-A port via an adapter or a Type-A to Type-C cable. So going USB-C allows you to get the best of both worlds, the out-of-the-box convenience with modern equipment and the compatibility with legacy devices when need be.

A Fist Full of USB Cables
Standard USB-Type B variants (clockwise from the bottom): USB-C, Type-B, Mini-B, Micro-B, Type-B SuperSpeed, Micro-B SuperSpeed.

2. Connection standard: How fast things connect

The connection standard determines how fast a connection is and what you can do with it.

For example, the USB 2.0 standard, determined by the USB Implementers Forum, allows for a connection speed of up to 480 Mbps, and you can also use it to charge a connected device.

We have two primary connection standards, USB and Thunderbolt.

Extra: Connection standard vs connection type

It’s important to note that the connection standard is independent of the connection type mentioned above.

For example, the USB4 is a protocol specification that defines the performance capabilities that can be implemented in a product. (In a way, it’s like a type of engine, like V6 or V8.)

That said, USB4 does not necessarily mean SuperSpeed USB, USB Type-C, USB Standard-A, Micro-USB, or any other USB cable or connector — these are attributes of a particular product. (This is like you can use the same engine in different types of vehicles, like cars vs. trucks.)

USB standards

Due to multiple name changes of the third USB generation, USB standards can be confusing. Currently, there are the following:

  • USB4: This is the latest USB standard that was once referred to as USB 4.0. This is the first USB that has built-in display protocals and, therefore, encompasses Thunderbolt 3. On top of that, it has the best naming convention. USB4 is avaiable in two variants.
    • USB4 20Gbps: 20Gbps a speed cap.
    • USB4 40Gbps: 40Gbps speed cap.
  • USB 3.2 with three variants:
    • Gen 2×2: Formerly USB 3.2, and is another upcoming USB standard despite the availability of USB4 — as of 2021, still very few devices on the market have it yet. Cap speed: 20Gbps.
    • Gen 2: Formerly USB 3.1 Gen 2, also called USB 3.1 at one point. By 2021, this is a mainstream in 2021. Cap speed: 10Gbps.
    • Gen 1: Formerly USB 3.1 Gen 1, also widely called USB 3.0. By 2021 this is the most popular USB standard with almost all existing devices supporting it. Cap speed: 5Gbps.
  • USB 2.0: Older standard that’s still quite popular. Cap speed: 480 Mbps.
  • USB 1.1: An ancient standard that’s obsolete. Cap speed: 12 Mbps.

To recap, so far, we’ve had USB 1.1 (obsolete), then USB 2.0 (fading away), then USB 3.2 (mainstream), then USB4 (latest) — forget about 3.0 or 3.1, and you’ll be less confused.

Now, keep in mind that USB 3.2 doesn’t exist just by itself but in one of three variations, including Gen 1, Gen 2, and Gen 2×2. (Gen = Generation.)

Generally, USB can also deliver power to a connected device. For this reason, most, if not all, portable drives don’t require a separate power adapter; they draw juice from the host. Via special software or driver, USB can also deliver sound and video signals but only at certain quality levels.

Note on USB cables and speeds

Note that the speeds mentioned above are theoretical. USB has crazy overheads, and the real-world sustained rates depend on the application.

That’s partly because the USB cable has relatively loose requirements and works as a dead wire.

Different manufacturers can make them however they see fit to serve their own products or so that they can sell them for cheap. As a result, most USB cables are considered “low-quality.”

Here’s a quick tip: Don’t expect a cheap generic USB cable to work well with all supported USB devices. It’s best to use the cable that accompanies the particular device.

Most importantly, in any case, you should expect the performance of a USB connection to be between half and 2 thirds of the standard numbers above.

USB vs. Thunderbolt: A brief history

You’ll note right away that the naming of USB 3.2 is a big mess. It’s a good thing that the USB Implementers Forum finally got its act together with USB4.

Official NameYear ReleasedFormer NamePort Type
 at Host
Port Type
 at Device
Backward
Compatibility
Ceiling
 Speed
USB 1.11998noneType-AType-BNone12 Mbps
USB 2.02000noneType-AType-B, USB-CUSB 1.1480 Mbps
USB 3.2 
Gen 1
2008USB 3.0 or 
USB 3.1 Gen 1
Type-A, USB-CType-B, USB-CUSB 2.0, USB 1.15 Gbps
Thunderbolt 2011NoneMini DisplayPortMini DisplayPortNone10 Gbps
USB 3.2 
Gen 2
2013USB 3.1 or 
USB 3.1 Gen 2
Type-A, USB-CType-B, USB-CUSB 3.2 Gen 1 
USB 2.0, USB 1.1
10 Gbps
Thunderbolt 22013NoneMini DisplayPortMini DisplayPortThunderbolt 20 Gbps
Thunderbolt 32015NoneUSB-CUSB-CUSB-C devices40 Gbps
USB 3.2 
Gen 2×2
2019USB 3.2USB-CUSB-CUSB 3.2 Gen 1/2
USB 2.0, USB 1.1
20 Gbps
USB4 20Gbps 2019USB 4.0USB-CUSB-CThunderbolt 3
USB-C devices
20 Gbps
USB4 40Gbps2019 USB 4.0 USB-CUSB-CThunderbolt 3 
USB-C devices
40 Gbps
Thunderbolt 4Late 2020NoneUSB-CUSB-CThunderbolt 3 
USB-C devices
40 Gbps
Thunderbolt 5TBDNoneUSB-CUSB-CThunderbolt 3
Thunderbolt 4
USB-C devices
80Gbps
Connection standard specifications: USB vs. Thunderbolt

Thunderbolt standards

Relatively young, Thunderbolt has been through three main revisions. Thunderbolt 4 was first announced in July 2020, but you won’t see it on any devices until late 2021 or even 2022.

That said, here is the state of Thunderbolt:

  • Original Thunderbolt: This standard uses the Mini DisplayPort port type and has the cap speed of 10Gbps.
  • Thunderbolt 2: It also uses Mini DisplayPort and has the cap speed of 20Gbps.
  • Thunderbolt 3: Uses USB-C port type. Cap speed: 40 Gbps.
  • Thunderbolt x: Going forward newer revesion (TB4, TB5, etc.) will aso use USB-C port type but eith higher speed and likely more feature.

Thunderbolt can do a lot more than USB. It can deliver ultra Hi-Def video/audio signals with high-speed data signals and works as a high wattage power delivery. You can also daisy-chain up to 7 devices together without signal degradation.

By the way, currently, a Thunderbolt 3 port supports the top speed of USB (20Gbps). Future Thunderbolt generations will continue to use USB-C port type and feature USB within.

Extra: Thunderbolt 3 vs Thunderbolt 4

It’s hard to put the finger on the differences between these two. Thunderbolt 3 can virtually do everything Thunderbolt 4 does — the two share the same ceiling speed of 40Gbps.

What sets the two apart is probably the stricter requirements for the TB4 certification. Specifically, Thunderbolt 3 requires a minimum PCIe bus speed of 16Gbps, while TB4 needs PCIe 32Gbps.

PCIe
Gen
Commercially AvailableRate per lane
(rounded)
x1 
Speed
x2
Speed
x4
Speed
x8
Speed
x16 Speed
120032 Gbps250 MB/s0.5 GB/s1.0 GB/s2 GB/s4.0 GB/s
220074 Gbps500 MB/s1 GB/s2.0 GB/s4 GB/s8.0 GB/s
320108 Gbps984.6 MB/s1.97 GB/s3.94 GB/s7.88 GB/s15.8 GB/s
4202016 Gbps1969 MB/s3.94 GB/s7.88 GB/s15.75 GB/s31.5 GB/s
5TBD32 Gbps3938 MB/s7.88 GB/s15.75 GB/s31.51 GB/s63 GB/s
PCI Express PCIe in brief
Note: 1 Gigabyte per second (GB/s) = 1000 Megabyte per second (MB/s) | 1 Gigabit per second (Gbps) = 125 MB/s

On top of that, TB4 also requires Intel VT-D-based direct memory access (DMA) protection and has some other minors improvements.

In shorts, TB4 mostly affects hardware makers who need to follow more stringent guidelines to be certified. TB3, on the other hand, offers more flexibility in hardware requirements (and cost) and might not have the same level of stability.

In other words, at the top, TB3 and TB4 products are the same. However, bottom-tier TB3 products sure are lesser than those of the lowest-end TB4.

From the user’s point of view, the two are pretty much the same.

Note on Thunderbolt cables and speeds

Thunderbolt has much better efficiency than USB. That’s partly because the TB cable itself is a device that requires power — it does more than just being a wire.

You can expect the sustained real-worlds speeds to be close to 90% of the numbers mentioned above. But, again, things depend on the particular application.

Conclusion

With lots of capabilities, the Thunderbolt is a standard initially designed to replace all other wired peripheral connections, including HDMI, DisplayPort, and, maybe, even USB.

But Thunderbolt is expensive — it requires extra hardware — and a bit complicated in licensing for hardware vendors to support.

It’s also worth noting that the way Intel has handled Thunderbolt — adding faster speed and more features — kind of makes it cease to be a “standard” and more of an umbrella “protocol” that wraps around a mess of confusing speeds, grades, and features.

My take is Thunderbolt might become counterintuitive at some point in terms of universal compatibility. It has too much of what people don’t need at the expense of cost and application restrictions.

For this reason, the loose, easy, and dirty USB has been winning and will continue to prevail in a popularity contest.

I guess that Thunderbolt and USB will completely converge at some point, as they have in the case of USB4 and Thunderbolt 3.

But even before then, the USB-C port type has already had enough reasons to reign supreme. And for this reason, from the general users’ perspective, the USB-C port type is all you need to really care about.

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14 thoughts on “Device Connections Explained: Thunderbolt or Not, It’s All about USB-C”

  1. Hi Dong
    I’d never heard of TB until buying a new Dell laptop and didn’t realise Type-C was so good (I’ve got it on my Samsung phone)

    So for me this was a brilliantly helpful article!
    Many thanks

    Reply
  2. Dong,
    I have a laptop that has TB3 can I attach a TB4 hub in it. It looks like it wouldn’t work, but TB4 says it’s compatible with TB3?

    Reply
    • It should work, Frank, unless your TB3 port doesn’t have the requirements of the TB4 hub (such as the power output) *and* the hub doesn’t have a compatibility mode. This is where TB has become convoluted, as I mentioned in the post.

      Reply
  3. Great stuff, Dong.
    But it isn’t all about data rate, it’s also about charging rate. I’m on my third (and apparently last) LG vXX phone, the v60. It supports Qualcomm’s proprietary QC 3 which will take a charge rate of as high as 2.5 A as verified by the excellent AccuBattery app. I also use a Uni-T USB charge tester for a sanity check which is a great, cheap device and with it I can see what other devices without the QC pull, and it’s typically <1.0A (depending on the age of the device.

    Reply
    • I agreed, Chuck. Totally. And that’s where TB is problematic because the cable itself requires power for itself — it is a device — it’s quite hard to factor it in. That said, USB is a much better alternative, up to USB 3.2.

      Reply
  4. Small thing, but this new version still says “USB 3.2 Gen 2×2: Formerly USB 3.2, and is the upcoming USB standard. Cap speed: 20Gbps.”

    Reply
    • That’s because it is still an upcoming standard, Jon. Most computers don’t even have it yet. 🙂 But nice catch, nonetheless. I rewrote that part for better clarity.

      Reply
  5. A quick question: I am planning on getting a new laptop as soon as Windows 11 comes preinstalled. Is it important to get Thunderbolt 4 as opposed to 3? What are the advantages of 4 over 3?

    Thanks
    Reuven

    Reply
    • As I mentioned in the post, Reuven, the two are pretty much the same. It doesn’t hurt to get TB4, but you might have to pay extra for it without much in return. I wouldn’t bother, especially when you’re using Windows.

      Reply
  6. I realize this article was written 2 years ago, but I still wanted to say THANKS! It was helpful and written in a way which was easy to understand. Thank you for knowing there are plenty of us out here who are NOT tech savvy and appreciate you ‘dummying it down’ for us.

    Reply
  7. I know you know this, but just as a reminder since it wasn’t mentioned in the article: USB4 is coming!! With 10, 20, and 40 gbps speeds. USB4 will be type C only, and some manufacturers may (or may not) include thunderbolt 3 into their USB4 solutions. Also, thunderbolt 3 has seen a tepid adoption in the industry in part because intel was charging a royalty for the technology. But intel has changed its mind and donated thunderbolt 3 to the USB-IF for implementation in USB4.

    Reply

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