A limit on number of USB hubs in Windows 7?

  • Thread starter Thread starter Yousuf Khan
  • Start date Start date
Y

Yousuf Khan

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'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
Click to expand...

Are they all powered hubs?
 
Yousuf Khan said:
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
Click to expand...

Go to Device Manager and right click on the root.
Select "Scan for hardware changes"
 
There's a limit, but it's pretty big, like 256 total devices, IIRC.
Click to expand...

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...
Click to expand...

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?
Click to expand...

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...
Click to expand...

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
 
Are they all powered hubs?
Click to expand...

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
 
So, how and where are each of your hubs plugged in to your computer?
Click to expand...

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
 
Go to Device Manager and right click on the root.
Select "Scan for hardware changes"
Click to expand...

Actually I've tried that before, and it only rediscovers anything after
I unplug and replug.

Yousuf Khan
 
Yousuf said:
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
Click to expand...

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.
 
Because I have intuition. If they are so good take them back and ask for
a refund and buy something else.
Click to expand...

Ah, I see, you use the same method of purchasing computer gear as you do
for ladies' purses?

Yousuf Khan
 
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
Click to expand...

Sounds like a flaky hub.
 
I haven't got the answer regarding the number of hubs.
But I have got the answer regarding the number of USB devices which can be connected to a single hub under Windows 7: 24.
That is the maximum number of wireless mice which can be connected with the multiple mice software by Microsoft: Mouse Mischief (Plug-in for PowerPoint 2010).
If 25 USB devices remain connected during power up/ down, the OS hangs - blue or black screen ...
 
Back
Top