A quick guide to USB endpoint limitations

Have you ever seen this message on your host Windows PC:

Or maybe your MacOS or Linux host has just failed to connect properly?

These operating systems don’t even notify you. If so, you’ve probably hit a USB endpoint limitation. It’s a brick wall of connectivity caused by exceeding your maximum number of possible endpoints or the endpoint memory of your host computer and/or USB hubs. And it can cause failed installs, a lot of time wasted and troubleshooting headaches. You can only connect a certain number of devices to your host computer at any one time, and that number will vary. Let’s explore how to find out more about your endpoints and how to increase them.

What is an endpoint?

Our very own USB expert (aka #USBGuy); our Director of Engineering, Mark Robson explains, “An endpoint is essentially a communication channel on a USB device. It acts as a buffer that allows data to be sent or received between the device and the host computer. Think of endpoints as data highways that manage how your device communicates with your system.”

Mark goes on to say, “every USB device—whether it’s a smartphone, tablet, computer, wearable (like smartwatches or headsets), camera, or microphone—uses endpoints to transmit and receive data. Each endpoint consumes bandwidth on your host system, typically using around 4KB per endpoint. However, there are only so many endpoints available on your computer’s USB host controllers, which can limit how many devices you can connect at once. The maximum number of USB endpoints a computer can support varies widely based on its USB host controller and system architecture.

USB 2 controllers typically support up to 96 endpoints. However, USB 3.0 controllers are more capable, often supporting up to 254 endpoints per controller. However, the actual number of endpoints you can use is also affected by how these controllers allocate resources among connected devices. Lastly, most systems have multiple USB controllers, so the total number of endpoints a computer can handle is the sum across all its controllers.

The number of endpoints used by each device varies depending on whether it’s operating in USB 2 or USB 3 mode. Devices running in USB 3 mode can require more endpoints due to their higher data transfer capabilities and advanced functionalities.

It’s important to note that endpoint availability is shared among all connected USB devices, so complex devices (like smartphones or cameras) that require many endpoints can quickly exhaust the limit.”

How many USB endpoints can you have?

What is the answer to how many though? Well, there’s no one answer. It’s different for all devices and computers. To find out how many things you have connected to your host computer via our USB hubs:

• Open the Cambrionix Connect application (download here) or talk directly to the Cambrionix Hub API (have a look at the API manual here)
• Click on the Cambrionix hub to scroll down to see how many are being used 
• Or click on the connected devices and it will tell you how much memory and endpoints are being used. It will also show what the maximum we’ve seen from that device is:

To see what your connected devices might use, have a look at this chart:

This table is accurate as of November 2024, but the always-live and updated version is here.

How do I get around USB endpoint limitations?

One way we can get around USB endpoint limitations is by using Thunderbolt. Inside your host computer, there are multiple USB controllers and those are what have these endpoint limits. So, when you connect a ThunderSync hub via the Thunderbolt port on your device instead, you can bypass these limits. That’s because our ThunderSync devices have multiple USB controllers of their own. Our hubs expand the number of controllers and therefore, the number of endpoints available to your host system through the unique ThunderSync technology. This means fewer limits, better connectivity, more stability and a competitive advantage for you.

For more on ThunderSync and its benefits, click here. Or if you need help to overcome your current USB endpoint limitations, fill out your details below: