You may find yourself surrounded by articles and opinions covering why Thunderbolt ports yield much faster speeds and more flexible connectivity than USB. That the technology does circles around any version of USB, including USB 3.2. Given such performance, this may lead to you questioning why Thunderbolt hasn’t simply replaced USB since Thunderbolt 3 and 4 (TB3/TB4) make use of the exact same port style. Questioning why computers aren’t littered with TB ports vs normal USB.
We have actually noticed this topic come up a lot lately as we venture ever so closer to TB4 becoming more popular with motherboards and laptop options soon to release this year. So, why don’t computers and laptops make use of additional TB ports if they are so darn useful? The answer is actually quite simple. At least, the next paragraph is. Breaking it down to dig deeper into what it all means might raise some confusion if you aren’t savvy with terms of the general technology of a motherboard (so bare with me).
The answer is that it all comes down to a limitation of data throughput and power everywhere else. As we move toward technology that can make use of such incredible transfer speeds and charging capabilities, we begin tapping into the PCIe slots/lanes on the motherboard to make it happen (to move all that data around between devices). This includes TB3 or TB4 as well as NVMe (SSDs). Since processors have a limited number of PCIe lanes they support, these technologies have to learn how to co-exist and share.
This is quickly becoming noticeable with the latest processors as they embrace new technologies like PCIe 4, TB4, and NVMe. Typically, 16 lanes are dedicated to the main video card slot (x16), and depending on the card you insert, it may have an effect on the slot below it (if there are two 16x slots). If you insert an 8x video card, the slot below it could become an 8x slot since both might be sharing the same 16 lanes. If you insert a 16x card, the slot below may become unusable in order to take advantage of these 16 lanes, else both slots may become 8x even if a 16x card has been inserted into both. Again, it’s all about balancing the available lanes the motherboard and processor are capable of supporting.
Then you have the additional PCIe slots (4x or 1x,) the systems have to offer, plus anything else like m.2 slots for NVMe drives (SSDs). You’ll notice that many motherboards that support NVMe via m.2 slots (typically located between the PCIe slots) will suffer changes to the PCIe slots when the m.2 slots are made use of. So if you insert an NVMe drive into one of these, one of the PCIe slots may become disabled as those lanes are now being used by the SSD within that m.2 slot. So now factor in how many TB ports you want on that system while still having a board that supports everything else. I mean, just look at what a single TB4 port can accomplish in the main image of this article above (with TB3 being able to accomplish quite a lot as well).
You might also like:
Top uses of the PCIe 1x slot on your motherboard
We are also just venturing into the world of PCIe 4, which is still in its infancy of support between processors. In fact, Intel is only now (this month) releasing processors that support PCIe 4. These chips/boards feature limited support so you’ll typically find that only the 16x slot(s) is/are 4.0 and everything else is 3.0 still. So the transition between the generation of these technologies can have a bit of effect on everything.
Next, you have the issue with power. TB3 and TB4 can provide a lot of power, capable of not only moving data at incredible speeds but being able to daisy chain a single port while also being able to provide power to those devices (including certain monitor models). PCIe can’t provide all of that power so TB3/TB4 will typically draw additional power via your power supply via a dedicated connection to its cable breakout/harness. So, even if you are adding TB ports via expansion cards for a desktop computer, you are running into certain limitations and requirements.
You can imagine how that last part plays heavily into the use of TB on laptops. Now you are looking to squeeze as much into a system as possible while also making it energy efficient to last long enough on a worthy battery charge. Laptops are designed to be mobile-friendly and not be tethered to an outlet all of the time. So if a laptop made use of three or four TB3 or TB4 ports that are actively being used, you can bet that battery is going to croak petty quickly (and that’s if it is rated to be able to put out that kind of power to begin with).
Finally, there is also a bonus variable of cost to the consumer. TB3 features a licensing fee as well as a fee to get a product certified before it can be sold as “TB3” capable. TB4 dropped the licensing fee and joined in with USB4 with a neat strategy, but the certification stage is still required before a product can be sold as having TB4. Then there is the level of motherboard and technology required to host TB, which is typically seen as enhanced or premium level boards. So making use of TB raises the cost to the consumer. Greater TB performance and support will also raise the cost to the consumer as everything else needs to be beefed up to handle it.
There are options out there that support additional PCIe lanes (28-48 lanes, for example). However, these fall into the enterprise side of the industry and a higher cost than what (most) consumers are looking to spend on a system (or the power bill to keep such a system running). This includes some of Intel’s Xeon solutions.
Ad: Thunderbolt 3 supported motherboards on Amazon
So that is why computers have a limited number of Thunderbolt ports. It all comes down to data throughput and power limitations (as well as the cost to the consumer). Eventually, everything else surrounding these technologies will grow and flourish all the same and we will look back at this and laugh (hopefully, sooner than later). Until then, we have to deal with sharing these data highway lanes between all of the technologies of the computer.
