How Many USBs Can You Plug In At Once?
in front of me are 127 USB devices the theoretical limit that is supported by a standard PC but USB has a dark secret as it turns out the real world limit is actually much much lower and the only way to find out what it is for sure is to just start plugging devices in which oh well I mean I guess we could just read the white paper on the architecture of the spec but that would be far less interesting for the people watching on YouTube so instead we're just going to start plugging things in and see what happens what do you do once you run out of ports I mean hubs obviously but can we just keep plugging in Hub after Hub after Hub until we hit it what is it and what is the Segway to our sponsor the ridge looking for a stylish and practical wallet the ridge wallet has got you covered its minimalist design allows you to carry your essential cars and cash without the bulk so check it out at the link below and use code Linus to save 10 off your purchase and get free shipping the first factor that limits how many USB devices you can connect to your computer is one you know quite well and that's the number of ports on the front and back of your PC but what you might not know is that most computers only have a single USB host controller and all of those ports are going to share not only that controller but that controller's bandwidth so when you have a USB 5 gigabit per second Port it's five gigabit per second shared with all the other ports on the controller now fortunately hitting a bandwidth limit is pretty uncommon most peripherals like mice or keyboards use a negligible amount of bandwidth however you can run into odd behavior if you have say for example a video capture device or a webcam this was really common with early generation VR headsets where the VR tracker sucked up so much bandwidth that users needed to install a second controller on an add-in card of course our question today isn't how much bandwidth can we push through one of these controllers it's how many devices can we connect to one so let's move beyond the limits of our mirror mortal rear i o ports I summon The Hub I haven't even plugged the Hub in yet and I think we're already getting kind of weird Behavior none of these whoa whoa this mouse is crazy hot wait heatedmouse.com oh it's a feature all right people unpowered hub now a mouse hey there it is Logitech gaming mouse now another Drive ah but this is interesting every Hub is actually two hubs see that we've got a USB 2 Hub and a USB 3 Hub and depending on what kind of devices we plug in they'll show up under either hubs like this one are an integral part of the various USB specifications they handle all the communication between devices that are plugged into them and the host systems that they're plugged into as well as handling bandwidth sharing the Hub will tell the system hey I'm a hub and the system adds that hub's address to the path of any devices that are plugged in down the chain when multiple hubs are used multiple addresses are added to the path so if Hub a for example is plugged into Port 4 of the host Hub B is plugged into Port 2 of Hub a and then a mouse is plugged into Port 1 of Hub B the address might read something like 0421 or 0 is the address of The controller's Root Hub powered or unpowered it doesn't change the addressing system however according to the USB spec a hub that is powered entirely by the port that it's plugged into like this one cannot allow this sort of daisy chaining according to the spec anyway as we are about to see however that is not the case here right look at this but why though because unpowered hubs are liars sometimes actually not just sometimes most of the time and if that shocks you well it shouldn't consider their predicament according to the spec only low power devices so devices that draw less than 100 milliamps are supposed to be used on hubs that are powered by the port itself and not by an external power brick so if people buy a spec compliant unpowered Hub they're going to be in for a rude shock when many of their devices I mean even mice with too many RGB lights won't work for some unclear reason so as a result manufacturers can either have mostly happy customers and with an out-of-spec product or they can have USB implementer Forum certification well Average Joe customer doesn't care about usb if certification they might not even know that they exist whose Castle is this they just want a hub that works with their devices and it usually will however draw too much current and your USB controller will shut down the connection from The Source hopefully before anything gets damaged should we try that why don't we plug the heated Mouse into this thing okay working now but what happens when we turn our heat to high oh wow this is still working somehow I need more power how about this k95 keyboard really how is this all still working at more brightness that was Max brightness let's plug into a USB 2 port that'll do it and really were you expecting this to work I mean no not really but time for another RGB keyboard two full RGB keyboards and a heated Mouse do we have any bigger unpowered hubs no these are the two unpowered hubs I could find most of our stuff seems to just be powered and it's plugged into a USB 2 Port which means that it's pulling at most two and a half Watts which is crazy that all that stuff just works okay what I suspect is that this motherboard is just like um I will deliver more than spec unbelievable I can't believe they just allow more power draw so that things function properly this will do it heated Mouse RGB keyboard and stream deck no it doesn't have the software is this I want it to light up full brightness oh wait hold on USB device not recognized last USB device you connected has malfunctioned yes we've overwhelmed it wow wow what the devil is that she real unhappy I suspect if we plug this directly into the back of the PC a H it would show up just fine Elgato stream deck XL there it is everything working perfectly but we take it back out of here and we plug it into our unpowered hub and boom problems suck says [ __ ] point is there's a solution to that powered USB hubs like this one from sabrinth that does a whopping 16 devices now something funky about these is that they are power mandatory hubs some are power optional remember that first one that I had over here it actually has a barrel Jack so it can operate as a powered Hub this one on the other hand is like uh-uh no can do where's my cable zip zilt NADA but plug in a 90 watt charger and hey there we go all right this is interesting we're going to talk about this later all the different hubs that are present here but first let's see if we can get our stream deck and our heated Mouse and our RGB keyboard running at the same time we gotta turn on those ports of course with these I can greatly expand my USB connectivity all I have to do is daisy chain my Hubs together which should give me pretty much Unlimited hubbery uh except for one small problem too many USB hubs a hub will not function when it's connected more than five hubs away from the root Port but this is only three hubs remember when we noticed that each of these one hubs was identifying as five hubs in software sort of okay USB hub chips can have up to seven Downstream facing ports or dfps most Hub chips have only four dfps so a manufacturer looking to make a big tough USB bar that doubles as a self-defense weapon could achieve their desired number of ports by doing what anyone else would by chaining them together this particular model from sabrin has one main chip with four dfps that each branch off into four more chips with four more dfps each that gives us a total of 16 ports Each of which are two hubs deep so if we put three of these together that's six hubs in a row of course all of this Hub into Hub tomfoolery was just an excuse for me to talk about Hub depth limitations the real way to plug in is many devices as we can is to plug each of our hubs into the back of our PC now we're only two hubs deep on every one of these ports meaning we can start loading things up I could use a couple of extra hands here boys I'm actually going to turn these off just so that I can do this we're not going to be able to use USB thumb drives forever though Windows gets kind of fussy about how many Drive letters a little signs so I'm just going to do one Hub worth of these start bringing over mice yeah why don't we have a mouse Hub a USB thumb drive hub and a keyboard Hub what do you guys think sound good we are up to 30 devices now and I gotta say good old USB you know we kind of take it for granted you know you just use it every day and don't think about it but it is shockingly robust are you guys um what are you guys doing with the keyboards over there uh we need to plug some in right now is what we need to do all right hit me with some cables cable plug these two in better believe it we've made it to 48 devices all of which are showing up correctly and while there is some weird Behavior Uh I can't click sometimes for example yep that's uh hold on maybe a different Mouse we'll click no um how about this no no that doesn't work but uh what about the Windows key oh uh control shift Escape hello oh yeah about uh could bring up task manager so that's good alt f4 anything buddy shoot okay let's go just One keyboard and one Mouse for a sec here why was I able to click on that one thing and not a different thing this is so weird okay yes we're back and come back all my pretties okay excellent now I have another hub there is a point to this we're on a different screen now and I'll show you why this is important let me just get everything lit back up here first it's at 1 14 right now we're at 172. uh uh this is not what I was expecting to happen but we have a total of 234 endpoints um Tanner yeah that's not what we were expecting to happen is it not at all I haven't found so much as a data sheet for a USB Root Hub that can handle more than 128. it's supposed to fail at 127. well 128. um it did not apparently the AMD chipset is just very powerful when it comes to the amount of USB it can handle yes more devices Tanner what is it supposed to do uh it's supposed to tell you that it's out of resources I see and were you ever actually able to create that condition tons of times cool it became something I could do in less than five minutes on both my laptop and the system I was testing on I see those are both Intel based systems and for some reason AMD just decided to go ham on the amount of USB they can handle starting with am4 but back then it was still limited to 128 and I expected it to be at least somewhere near 128 still but no it what are we at right now 304. let's go World new world record some of hubs and devices is 101 right now we are getting dangerously close to the goal we set out at the beginning of the video and we haven't even pulled out the USB innator yet I will be very disappointed if I don't need this it's a theoretical limit of xhci is like 8 000.
but how often do we reach theoretical limits for these things I haven't been able to get anywhere near it without things breaking and yet here we are with AMD just tanking it surely this final Hub will be enough he said not really convinced ah this video is completely off the rails now there were rails there was a script there was a plan weeks of testing and then we just happened to grab an AMD system 106. remember because there's five hubs in here right plus the one thing I replugged back in uh okay I'm just gonna start finding plugs and plugging them into things why thank you good sir 337 endpoints wait oh oh we just lost a bunch we're down to 270 endpoints all of a sudden the keyboards are dead whoa we are losing devices left and right here did we just completely oh wow they're coming back okay wow this is not what you want to see well cool at any rate here's screen capture of the normal way that this happens that Tanner will get later and this is also a thing that can happen when you have too many endpoints allow me to explain it's not a device limit or a power limit or a bandwidth limit this is an end point limit an end point is a data pipe between the host and the device and a device will typically have multiple endpoints for things like configuration occasional small low latency data transfer non-time critical large data transfer and continuous data flow for things like microphones or cameras now remember when I said that well they're all buried now but these hubs were actually five hubs well that was half true they are five USB 3 hubs and they are also five USB 2 hubs for a total of 10 hubs each Hub uses two endpoints for a total of 20. now technically xhci extended host control protocol supports up to 31 end points per device which assuming a reasonable 127 device limit like we encountered in our testing is nearly 4 000 endpoints that's enough endpoints to fill up a tech Sac from ltdstore.com but you're not going to be able to actually hit that limit with Modern Hardware because controllers almost always have a limit of 64 to 128 endpoints typically settling on around 96 except that this one didn't it had like over 300 or something but that doesn't matter because we are still going to get to our goal of plugging in 128 devices with the USB animator it should actually behave less flakier than this maybe don't make promises you can't keep the one with all the USB drives in it is flipping hot like unhappy wow ow you know it kind of is a good representation of the difference in philosophy between Intel and AMD Intel has a tendency to just say this is what we know we can support reasonably well and just know you actually may not have any more than that whereas AMD tends to be kind of more YOLO like I don't know see what happens we're not going to put a limit on it what you are looking at here is an Asus mining motherboard not because we're doing any Bitcoin mining or anything like that but because we want a whole bunch of pcie by one slot plugged into a whole bunch of these little mining daughter boards that instead of being loaded up with graphics cards are loaded up with USB controller cards in total I believe we have 30 total USB controllers meaning that we are going to be nowhere near any kind of endpoint limit Shenanigans to get to our 127 devices from the outside the usbnator is very similar to what we were just doing we've got the sabrant 16 Port hubs and we're going to plug them into ports in the back of our computer but it's these ports that make this system different Star Tech sent over two different kinds of USB controller cards these ones with seven plugs and these ones with four and believe it or not the ones with four plugs are actually better than the ones with seven and that's because and if you've been paying close attention you'll know why this matters four of these ports namely the top ones are running off of an integrated Hub meaning that it would be much easier to hit an end point limit using these so for example if you had a couple more multi-port hubs and then one of these multi-display adapter things it would work in any of these bottom three which are directly connected to the controller but would cease to work if it was connected to one of the top four that is not true of our four port cards each of these is running off of its own controller meaning that the theoretical maximum number of endpoints going into just one of these cards would be 508 or something like that assuming each of these can do 127 endpoints what that means is that if all goes according to plan it should be basically impossible for us to reach an end point limit on this system I say we power the thing on all right because the first thing that we need to do is uh is verify which of these cards currently feels like working ah it's not the card's fault it's the risers right mining stuff definitely reliable oh so reliable this one has no lights yeah this one has no lights that's okay I can work with that I regret taking the approach we did last time why how many total drives did you say that you could handle as many as there are letters in the alphabet but really the problem is when a whole bunch of them connect at the same time then Windows tries and give tries to give the drive letter to multiple drives at once sick it is time to painstakingly plug in 127 USB devices how are we doing here how are we doing for endpoints boys oh we're we're at 56 total peripherals end points are going to be just based on the controller itself so we've got multiple controllers but yeah we're at 56 56 and 122 standard hubs not bad let's do more we are up to 86 peripheral devices the question is are they still functioning at all let's do my caps lock test so you should be able to kind of see them going going nuts okay what about the Windows key wow okay with all these controllers it's actually still kind of working can I can I click on something yes very nice more thumb drives I am uh I'm getting kind of nervous about the lean going on here like that is that is some pizza level almost and there is a single strip of tape holding these on it's good tape but Ah that's 16 ports worth of stress we're at 100 devices right now 100 devices let's go I have to say my side much more organized I did take the only rack though yeah we have a mouse infestation 104 are any of these not lit up oh that's that heated one uh weirds me out man oh crap something is depressed uh oh sorry no no not that kind of depressed oh are some of the ports not powered or something not power on this okay no there's no exactly oh okay what are we up to now Colin 112. oh we're so close 113. come on that didn't count that also didn't count oh we're down we're down to 110. okay what about this one oh no oh no oh I just saw keyboard lose power I wonder if this is more of a driver level limit just trying to manage all of these flipping device what does our CPU usage look like look at my cursor now just hold on a gosh darn second here oh okay it's not exactly a super powerful CPU it's only a quad core but we were pulling 60 when I opened this and it's sitting at 30 40 percent now just doing nothing while I'm disappointed that we couldn't get to 127 concurrent devices we learned a lot along the way and in fact I have had multiple times in the past when I've run into issues that would have been caused by these kinds of topology limitations that just I didn't understand in the past and now I will so the main things to take away here are that if you're using a hub you're going to want to connect that directly to the root controller and if you're using an unpowered Hub hey it might be running out of spec so make sure you're only plugging in low power devices or get yourself a powered Hub we're down to 99 guys I think she kind of take it anymore just like I can I take it anymore not telling you about our sponsor SolidWorks listen up makers hobbyists and tinkerers there's now an affordable way to use SolidWorks 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2023-08-15 03:43
