A limit on number of USB hubs in Windows 7?

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

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)

In article ,
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

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

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

Microsoft Windows MVP
Windows Live Mail 2010 (15.3.2804.0607) in Win7 Ultimate x64

"Yousuf Khan" wrote in message ...

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

"Yousuf Khan" wrote in message
...
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

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

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

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

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

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 ~