USB + Thunderbolt = What?

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As you probably know, I have moved onto using a hateful 2017 MacBook Pro with Touchbar, on which there are only Thunderbolt 3 ports, for power and data. Incidentally, I have also been using a Samsung Galaxy S8 for a while, and it has USB-C port for power and data. Why incidentally? Well, Thunderbolt 3 and USB-C share the same port design, so physical-connection wise, they are interchangeable, meaning that I can use my phone charger to (extremely slowly) charge up my laptop, and use my laptop charger to charge up my phone. Convenient, right? Yes and no. This blog entry will take you through the confusing hell that is USB-C and Thunderbolt 3.

Let’s start on the history of Thunderbolt. Thunderbolt was collaboratively developed by Intel and Apple, and as far as I know, was first unveiled by Apple on their MacBook Pro line of laptops, supporting bandwidth up to 10Gb/s. Thunderbolt 1 and 2 share the same physical port design as the mini DisplayPort (mDP), but can carry signals other than audio and visual ones, such as ethernet, or USB, or FireWire, or whatever adapter you can buy for it. That’s cool – as long as you’ve got the adapters for it. In fact, this was one of the major criticisms of the first retina MacBook Pro – its lack of ethernet and FireWire ports, for example. However Apple “resolved” this issue by including super fast WiFi card and releasing Thunderbolt-to-Ethernet and Thunderbolt-To-FireWire adapters, which worked brilliantly. Then, Apple released Thunderbolt 2, which now has twice the bandwidth of Thunderbolt 1 at 20Gb/s. It used the same design, so nobody noticed or cared.

Before I get onto Thunderbolt 3, let me remind you of what USB’s history is like. I am not overly familiar with the USB Implementers Forum (USB-IF) and their work, but as far as I know, they developed the USB protocol, which is extremely popular these days amongst consumers. If you have a relatively complicated communication-style digital device – a camera, a phone, smart watches, smart glasses, printers, WiFi routers, it is extremely likely that it implements the USB protocol in some way. USB 1.0 was introduced in 1996 supporting a painfully slow 12Mb/s bandwidth, using the almost universally recognised rectangular non-reversible USB plug. This plug is the end that normally goes into computers, and is called the Standard USB socket, or USB Type A. You know the kind of squareish ports that you normally find at the back of printers? They are USB Type B. These are just different types of plugs. They are practically the same. USB 2.0 came in 2001, supporting up to 480Mb/s bandwidth, using the same plugs as well as adding some new designs to make it more friendly with portable devices (the mini and micro USB designs that we are familiar with). USB 3.0 came in 2011, supporting up to 5Gb/s of bandwidth (this is half of what Thunderbolt 1 could carry). The plugs of USB 3.0 remained mostly identical, but typically in blue to indicate that it’s got more pins inside the plugs in order to support the higher bandwidth. They are also completely backward compatible with USB 2.0 plugs.

Now – USB C and Thunderbolt 3. USB C’s formal name is USB Type C. The reason for this is the same as the reason that USB Type A and USB Type B are named so – they are physical sockets. They do not dictate the protocol that’s carried through the cable. If you are talking about the fastest USB protocol available out there, it is called USB 3.2, which supports up to 20Gb/s of bandwidth (the same as Thunderbolt 2). It is very important to get the distinction between USB Type C and USB 3.2. One is the socket, and one is the protocol. Thunderbolt 3 utilises the USB Type C socket, but implements the Thunderbolt 3 protocol. Apple confuses this even more by throwing in an additional “Charging Cable”, which looks like USB C, smells like USB C, plugs in like USB C, but doesn’t carry any data, so it can only be used for charging the laptop, and whatever devices you have which has the USB C port and a battery.

So, to summarise: Thunderbolt 3 uses the USB Type C socket but implements its own protocol which supports up to 40Gb/s in bandwidth, and can also carry power, audio, video, and ethernet natively, as well as PCIe lanes which gives you support of external GPUs. USB 3.2 also uses the USB Type C socket but uses USB protocol, which supports up to 20Gb/s in bandwidth, only for data and some power. Simple right? No. Did you know, that USB 2.0 protocol can also be implemented through the USB C socket? Yeah, that’s right. Plugging in a USB C device doesn’t mean you get the latest and fastest speed. Is that confusing enough? Hang on: remember the Apple charging cable that I talked about in the previous paragraph? It implements what’s called the USB Power Delivery (USB-PD) protocol, which allows a compatible USB C cable to carry 100W of power. Note that this is different from the Thunderbolt 3’s power carry-through, but some Thunderbolt 3 controllers are compatible with USB-PD… Just.. wow.

What a mess.

So let’s look at Apple – “It just works!“. Or rather, “It worked before…“. Surely, they have come up with a way of simplifying this whole thing, right? Nope. Their new MacBook Pros, all have Thunderbolt 3 ports, but only on the 15 inch ones does each port have the full 40Gb/s bandwidth. On the 13 inch MacBook Pros, some of the ports share bandwidth. Their new MacBook, which has one USB Type C port, implements the USB 3.1 protocol, which means none of the accessories specifically designed for Thunderbolt 3 protocol works, despite the fact that they can be plugged in. At least they are still consistent with their Lightning port across their mobile devices.

Guys, before buying a high end accessory using USB C, do some decent research on if your device is compatible with it. It’s such a minefield out there for USB C devices and they are very easily trod on.

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