A limit on number of USB hubs in Windows 7?
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From: Yousuf Khan on 6 Aug 2010 00:44 On 05/08/2010 9:44 PM, Gene E. Bloch wrote: > On Thu, 05 Aug 2010 21:14:13 -0400, Yousuf Khan wrote: > >> I've got three 4-port hubs on my system. From time to time after a >> reboot, some of them don't enumerate properly, and you have to unplug >> and replug them. Is there some way in software to get Windows to rescan >> them? Of course that won't do any good if the USB hub that your mouse >> and keyboard are on is the one that doesn't get enumerated properly, but >> I'm tired of reaching into the back to unplug them. >> >> Also is there a known limit on how many USB devices that can be put into >> a single machine? I have at least over a dozen USB devices connected at >> a time usually, sometimes more. >> >> Yousuf Khan > > There's a limit, but it's pretty big, like 256 total devices, IIRC. Yeah, but that would be the official specification limit. I'm thinking more along the lines of the unofficial "real" limits. It also seems to be operating system dependent. Sometimes Windows XP or Linux seem to have less trouble seeing these hubs, sometimes not. This is all on the same machine, of course. > Hubs shouldn't matter. Four ports on a hub shouldn't be different from 4 > ports without a hub, again pleading IIRC... I even had a 7 port hub once, but that was a nightmare, it had the worst problems of them all being enumerated. The 7 port hubs are also internally daisy-chained, where one 4 port hub plugs into another 4 port hub, so I assumed it was due to this. > But for some reason USB hubs don't always play well with every device or > every computer. Maybe your variable performance depends on the whole > constellation of what is plugged into each hub on a particular Tuesday? That's basically the best way to describe it. :) > I can't get into Safe Mode on this computer if I have my mouse and keyboard > plugged into a hub, even with one keyboard I have where the mouse port is > on the keyboard... I also seem to have trouble getting some of my hubs to show up as USB 2.0 hubs, meaning working at 480-Mbps. They are all listed as USB 2.0 hubs but usually two of them seem to fall back down to the USB 1.1 15-Mbps speed. One will always show up at the full 480-Mbps speed, but the other two will go back to lower speeds. Yousuf Khan
From: Yousuf Khan on 6 Aug 2010 00:48 On 05/08/2010 10:09 PM, Al Dykes wrote: > Are they all powered hubs? No, one of them was, and that was the one with the biggest problems. The problems got slightly better when I removed the power cord from it. When it was self-powered, eventually it started crashing the machine. Not right away, but the problems got worse and worse until the machine got unstable and crashed. When I removed the power cord from it, it would just sometimes fail to enumerate, but it wouldn't crash the machine. Yousuf Khan
From: Yousuf Khan on 6 Aug 2010 00:57 On 05/08/2010 11:14 PM, R. C. White wrote: > So, how and where are each of your hubs plugged in to your computer? All of the USB hubs are connected directly through the motherboard's own USB ports, no separate add-in USB card involved here. Yousuf Khan
From: Yousuf Khan on 6 Aug 2010 00:58 On 06/08/2010 12:05 AM, Andrew wrote: > Go to Device Manager and right click on the root. > Select "Scan for hardware changes" Actually I've tried that before, and it only rediscovers anything after I unplug and replug. Yousuf Khan
From: "Dave "Crash" Dummy" on 6 Aug 2010 07:07
Yousuf Khan wrote: > I've got three 4-port hubs on my system. From time to time after a > reboot, some of them don't enumerate properly, and you have to unplug > and replug them. Is there some way in software to get Windows to > rescan them? Of course that won't do any good if the USB hub that > your mouse and keyboard are on is the one that doesn't get enumerated > properly, but I'm tired of reaching into the back to unplug them. > > Also is there a known limit on how many USB devices that can be put > into a single machine? I have at least over a dozen USB devices > connected at a time usually, sometimes more. > > Yousuf Khan I don't know squat about USB, but you might avoid the mouse/keyboard uncertainty by using the PS/2 connectors (if available) for them, instead. -- Crash "Facts are stubborn things, but statistics are more pliable." ~ Laurence J. Peter ~ |