How Many USBs Can You Plug In At Once?

This actually makes me appreciate the USB standard. Not only the fact you can just plug anything into it and expect it to work 99,9% of the time without any additional input, but also the fact that everyone just agreed that this is something we're going to be using on just about everything.

These limit finding videos are great for understanding our pcs more without having to go out and figure it out every single time.

Imagine how many times Linus had to turn USB connectors to get them to actually plug in. Truly a dedicated man.

I love how unscripted this episode is, and I do mean this 10/10. Please do more vids like this!

Linus and his team doing something completely unreasonable but still somewhat educational is my favourite type of content

For those who don't know, USB Tree View is the OP GOAT program for this stuff. It shows you all connected devices and their level so that you can diagnose issues. If you've ever had the annoying reconnecting USB device that keeps chirping its connection sound on and off, this is the tool to use. It'll highlight funky devices just as it did in this video.

I think the fact that you could plug in more than 128 devices is a relatively recent thing potentially starting at the 3000 series CPUs. I was running into USB issues on first gen Ryzen and I wasn't anywhere close to those numbers and I was having many of my peripherals turn off and then turn back on like they were reset on the addressing end. I added an internal USB controller card and that completely solved my issue.

Some powered hubs also had this rather dangerous flaw in that it connects directly to the VBUS pin to the host, so it can backfeed the power to the computer, which can damages the controller and sometimes the entire computer if it was a laptops or all in ones. BigClive has a video about this that explains it pretty well.

As a USB4 System Validation Engineer at Intel I found this video super interesting ,entertaining and educational. Great job Linus 👏

The real question is how many USB devices can Linus drop at once?

Linus did a good job explaining the different limitations imposed by the USB spec, but there is one more he didn't talk about: time. More specifically, scheduling of the USB request blocks inside a USB frame that's sent out, at most, once every millisecond (in the case of USB 2.0 at least, don't know if they raised it in later versions, but I don't think so). He mentioned the four types of endpoints: ones for configuration (Control), rapid but short message transfer (Interrupt), large data (Bulk) and continuous transfer (Isochronous). What he didn't talk about is that you can't just mix'n'match them willy-nilly, because there's a limit of how much of the frame each of these types of endpoints IN TOTAL are allowed to occupy. For instance, IIRC the limit for Interrupt types is 10%. This endpoint type is used by keyboards, mice, game controllers etc., so if you only have these devices in your system, you will effectively only be able to use at most 10% of the full bandwidth of USB.

I’ve had issues with plugging in too many hubs rather than too many devices which is interesting. Having the same amount of devices plugged into two hubs seems to work better than having them plugged into 4 different hubs. Also some hubs work almost flawlessly whereas others just keep dropping out when I connect thumb drives to them but peripherals work fine… USB stability, even more than the instantaneous number of devices you can have plugged in, is a big issue and it would be worthwhile to investigate stability in a seperate video. I will say that having a seperate usb controller via pcie definitely improves stability! I’ve noticed that. But when I plug in multiple external hard drives I have significant problems with them just disconnecting intermittently even if they are on seperate controllers (this happens more often under high bandwidth usage but also seems to happen even if I’m just using the drive a little bit??). I’ve noticed this issue on different devices; my old Dell intel 7th gen i7 laptop and on my X99 5820k PC. 4 port powered hubs seem more stable than 7 port powered hubs and 7 is more stable than 13 port hubs; but I have another specific 8 port hub that isn’t sold anymore and for some reason is super stable. Maybe stability varies on vendor or newness of technology like Linus noticed on AMD vs Intel. I wonder if there’s a measurable difference on USB stability and % uptime on Windows vs Mac or from vendor to vendor

(22:46) Linus - "Oh, crap, something is depressed." Tanner - "Uh, sorry." Gotta love Tanner

Every so often I get re-amazed by USB. I started using computers near the end of the 80s on a DOS machine and the hot-swappable, plug and play nature of USB really changed the game.

Very informative. Love that with Linus not knowing it was a heated mouse. 😁

At one of my previous jobs, we had devices with test harnesses, and the test harness PC would often run out of USB endpoints, so we had to run the harness machine with the Intel XHCI disabled, so the ports went to the two EHCI controllers instead. But then Intel removed the EHCI controllers from later chipsets. It seemed like Intel's limit was 64 or so, or maybe even less than that.

i stopped working in traditional IT departments way before it was "cool" this channel is a gem for old timey IT guys who miss the crazy IT department shenanigans we would do in the server room on off days. thanks for these!

I don’t know what’s more impressive, the fact it (almost) handled 127 USB devices, or the fact they were able to find 127 devices around the office that hadn’t already been stolen (as we’ve seen is a common theme from $5000 tech upgrade videos.)

Just wow! This has got to be one of your best videos I have seen yet. I learned so much about usb.

A fantastic hub! Have had one for the last couple years and the speed is great and not one issue at all.... A great video!