How do I connect two displays to My Mac?
This is a something that many people, understandably, struggle with. There are approximately 45 Billion display adapters, video cables, docks and hubs. Some Macs have 2 Thunderbolt ports. Others have 4. Some have USB, some have Thunderbolt. What about USB docks? Why are some $20 and others are $200?
I went though this myself a few months ago when I deiced to buy a second monitor for my computer. I needed a way to connect two displays and a bunch of other devices into a computer that only had two ports. A hub was the obvious answer – but finding a decent one took some research.
I wrote this guide so that others do not have to suffer through reading endless clickbait articles filled with outdated and contradictory information. There are a few recommended docks at the end of this post. I’m not affiliated with these companies in any way, and I don’t make a commission if you choose to buy one. They are just the docks that I think will work well for most people, and are made by companies with good reliability track records.
What is dock and why would I want one?
A USB or Thunderbolt dock is a piece of hardware that lets you connect multiple devices to your computer using a single cable. Most docks a few USB ports, an SD card reader, an ethernet connection, and video output. Higher end docks can also charge your laptop and have connections for multiple 4K monitors.
Aside from adding extra ports to your setup, a dock reduces (and usually removes) the need to use various adapters and cables for all your accessories.
What’s difference between a USB dock and a Thunderbolt Dock?
There are USB-C docks and Thunderbolt docks. This is confusing since Thunderbolt and USB-C cables look identical. In actuality, thunderbolt is a type of USB-C cable. The term “USB-C” only refers to the shape of the connector but doesn’t tell you anything about the it’s speed. Conversely, the term “USB 3.0” refers to the cable’s speed , but doesn’t tell you anything about its shape. In short: all Thunderbolt cables and USB-C cables, but not all USB-C cables are Thunderbolt cables.
USB 3 cables come in three different speeds: a 5Gbps version, a 10Gbps version, and a 20Gbps version. This doesn’t matter very much other than to point out that USB cables have one of the worst naming conventions of any technology, and it’s very easy to buy the wrong cable. This is mostly a concern for higher end docks. If you want to feel insane, read the wikipedia article on USB standards.
Here’s a simplified table that breaks down all the various types of USB-C cables
|Speed||Technical name||Common Name||Video Output||Usage|
|5 Gbps||USB 3.2 Gen 1||USB Superspeed USB||Sometimes||USB Hub|
|10 Gbps||USB 3.2 Gen 2||USB Superspeed USB 10Gbps||Sometimes||USB Docks|
|20 Gbps||USB 3.2 Gen 2×2||USB Superspeed USB 20gbps||Sometimes||USB Docks|
|40 Gbps||Thunderbolt 3||Thunderbolt 3||Yes||Thunderbolt Dock|
|40 Gbps||USB 4.0||USB4||Yes||USB4 Docks|
USB3 and Video Output
Sending video over USB 3 a cable and dock with a feature called alt-mode. Alt-mode accessories are wired differently than their non-alt-mode counterparts. Support for this feature is optional and it’s up to accessory manufacturers to add it to their docks and cables.The reality is that this feature if often poorly implemented and poorly documented. If you’ve ever had problems connecting a display to a USB dock, this is probably the cause.
Using a display with a non-alt-mode dock requires a video adapter. Apple sells a USB-C Digital AV Multiport Adapter for $70.
Thunderbolt 3 supports video output without the need for special cables or video adapters. If you Mac was released after 2017 it probably has Thunderbolt, but you can find the full list of Thunderbolt equipped Macs here:Apple Support – Identify the ports on your Mac.
Which type of dock should I choose?
You should buy a Thunderbolt 3 dock if any of these apply to you:
- You want to connect a ton of high speed devices to your computer. High speed devices include things like 4K welcomes, external SSD drives and external RAID enclosures. Some really fast external hard drives use Thunderbolt.
- You want to use multiple 4K monitors.
- You want to use USB-C Monitor(s)
- You want to buy your way out of the hell of USB-C labyrinth
You should buy a USB dock if any of these apply to you:
- You don’t need dual monitor support
- Thunderbolt docks are not in your budget
- You plan on connecting fewer than 10 devices. USB docks are fast enough for external SSDs, but probably not a great option for RAID enclosures.
Thunderbolt Dock Recommendation
My Recommendation: Caldigit TS3 Plus Thunderbolt Dock – $250 USD
If spending $250 is within your budget, this is the dock you should get. It has enough ports whatever you throw at it. It’s also one of the few docks that supports USB-C monitors like the LG UltraFine. This is the dock I purchased for myself I recommend it without reservation.
If you have a Mac with an M1 processor, read the caveats section at the bottom of this post
USB Dock Recommendations
- Belkin USB-C Express Dock $150 USD – has almost as many ports as the Caldigit Dock. Supports a single 4k monitor or two standard definition monitors. Will charge your laptop.
- Caldigit SOHO USB Dock ($100) – Fewer ports than the Belkin dock. Supports a single 4K monitor or two standard definition monitors. Will charge your laptop. This is a pretty new product so there aren’t many reviews yet.
- Anker 5-in-1 USB Adapter – ($35 USD) – This hub will give you ethernet and a few USB ports. Anker sells a few different varieties of this model. I recommend looking at their other hubs and choosing the model that best fits your daily needs. This hub also supports HDMI displays – but your mileage may vary in the success department. See the section about USB-C Alt mode above.
Caveat: M1 Macs
The new M1 MacBook Pro and MacBook Air can only support one external monitor. The M1 Mac mini can support a single display over Thunderbolt and a second display over HDMI.
The CalDigit USB Pro Dock ($249) can support two external displays on M1 Macs. That being said, I haven’t verified this myself. If anyone owns an M1 Mac and uses this dock please let us know how it’s working out.
Other Resources / Guides
- I recommend reading these the Wirecutter reviews for Thunderbolt Docks and USB docks. Both articles are updated regularly and the recommendations in this post might be outdated by the time you read it.
- Apple Support – About the USB Ports on your Mac – This article proves a nice summary of different USB specifications
- Adapters for the Thunderbolt 3 or USB-C port on your Mac or iPad Pro – This article can help you find the right adapters. Useful in general, not just for docks and hubs.
- Apple Support – Use external monitors with your Mac
- I originally wrote this post on r/applehelp. You can see the original post here