A limit on number of USB hubs in Windows 7?
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From: Yousuf Khan on 5 Aug 2010 21:14 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
From: Gene E. Bloch on 5 Aug 2010 21:44 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. Hubs shouldn't matter. Four ports on a hub shouldn't be different from 4 ports without a hub, again pleading IIRC... 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? 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... -- Gene E. Bloch (Stumbling Bloch)
From: Al Dykes on 5 Aug 2010 22:09 In article <4c5b61e6$1(a)news.bnb-lp.com>, Yousuf Khan <bbbl67(a)spammenot.yahoo.com> 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 Are they all powered hubs? -- Al Dykes News is something someone wants to suppress, everything else is advertising. - Lord Northcliffe, publisher of the Daily Mail
From: R. C. White on 5 Aug 2010 23:14 Hi, Yousuf. Like Gene, I can't recall for sure but I think the limit is 127 USB devices. And like Al, I wonder about power to - and through - the hubs. My own experience was with my wireless desktop (keyboard and mouse). They use the 2.4 GHz transceiver, which plugs into a USB port. When I plugged it into my only 4-port hub, the keyboard worked fine - until time to reboot, when there was no communication with the keyboard during startup, making it impossible to choose the Windows version to dual-boot. So I moved the transceiver to the back of the computer, plugging it into a USB port directly on the motherboard. Then I could dual-boot just fine - but the keyboard often went to sleep right in the middle of typing a message like this post. It would seem dead for about 2 minutes, then resume normal performance. After trying many other fixes, I finally realized that the hub's connection was to an add-on USB on a PCI card. So I moved the hub's USB to that mainboard USB port and put the keyboard transceiver into the hub again. Problem solved! ;<) While I haven't tried to do the arithmetic for the amount of power and how it gets divided, I suspect that the hub was not getting enough power from the add-on card to satisfy the keyboard. Or the hub couldn't handle the connection until Windows started and loaded its driver. In other words, the number of USB devices was not a problem (there are no more than a half-dozen total on my system), but the connection pathway from the mainboard to the device created a partial roadblock. The more-direct connection provides more power, and it probably also simplifies the data pathway. So, how and where are each of your hubs plugged in to your computer? RC -- R. C. White, CPA San Marcos, TX rc(a)grandecom.net Microsoft Windows MVP Windows Live Mail 2010 (15.3.2804.0607) in Win7 Ultimate x64 "Yousuf Khan" wrote in message news:4c5b61e6$1(a)news.bnb-lp.com... 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
From: Andrew on 6 Aug 2010 00:05
"Yousuf Khan" <bbbl67(a)spammenot.yahoo.com> wrote in message news:4c5b61e6$1(a)news.bnb-lp.com... > 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 Go to Device Manager and right click on the root. Select "Scan for hardware changes" -- Andrew |