On "business class" PC's, is it safe to assume the USB2 ports
(front and back -- typically 4 or 5, total?) are handled by one
controller and the USB3 ports by another?
And, more specifically, that power supplied to the devices
in each class are handled independant of each other?-a (i.e.,
USB3 having more power delivery capability than USB2).
Finally, is the power handling done with external (to the
controller) FETs or passed directly through (particularly on
the USB2 ports)?
SWMBO's legacy desktop has developed a power problem
with the USB2 ports (front and back).-a If power is passed
internal to the controller, then it's just not worth my time
to even open the case...
On "business class" PC's, is it safe to assume the USB2 ports
(front and back -- typically 4 or 5, total?) are handled by one
controller and the USB3 ports by another?
And, more specifically, that power supplied to the devices
in each class are handled independant of each other?-a (i.e.,
USB3 having more power delivery capability than USB2).
Finally, is the power handling done with external (to the
controller) FETs or passed directly through (particularly on
the USB2 ports)?
SWMBO's legacy desktop has developed a power problem
with the USB2 ports (front and back).-a If power is passed
internal to the controller, then it's just not worth my time
to even open the case...
On 8/15/26 05:40, Don Y wrote:
On "business class" PC's, is it safe to assume the USB2 ports
(front and back -- typically 4 or 5, total?) are handled by one
controller and the USB3 ports by another?
And, more specifically, that power supplied to the devices
in each class are handled independant of each other?-a (i.e.,
USB3 having more power delivery capability than USB2).
Finally, is the power handling done with external (to the
controller) FETs or passed directly through (particularly on
the USB2 ports)?
SWMBO's legacy desktop has developed a power problem
with the USB2 ports (front and back).-a If power is passed
internal to the controller, then it's just not worth my time
to even open the case...
you should able to see how it is connected in the OS, devicemanager on windows,
usbview et.al. in linux
I think everything but the cheapest stuff will have a load switch per port
On "business class" PC's, is it safe to assume the USB2 ports
(front and back -- typically 4 or 5, total?) are handled by one
controller and the USB3 ports by another?
It probably depends on age and number of USB ports.
Some of mine have two USB controllers one for the set of four or six on the back and one for the pair on the front panel.
And, more specifically, that power supplied to the devices
in each class are handled independant of each other?-a (i.e.,
USB3 having more power delivery capability than USB2).
When USB3 was new then almost certainly a separate device but in the latest generation of systems I honestly don't know.
Finally, is the power handling done with external (to the
controller) FETs or passed directly through (particularly on
the USB2 ports)?
On USB2 I suspect mostly they are pass through. USB3 can use higher currents and voltages that may be done by an external FET.
SWMBO's legacy desktop has developed a power problem
with the USB2 ports (front and back).-a If power is passed
internal to the controller, then it's just not worth my time
to even open the case...
Might be easier to interpose a powered hub between the offending ports and whatever you want to connect as a means of extending its life.
On "business class" PC's, is it safe to assume the USB2 ports
(front and back -- typically 4 or 5, total?) are handled by one
controller and the USB3 ports by another?
It probably depends on age and number of USB ports.
Some of mine have two USB controllers one for the set of four or six
on the back and one for the pair on the front panel.
There are a mixture of USB2 & USB3 ports in each location.
AFAIK, controllers are USB2 (EHCI) or USB3 (XHCI); while
the XHCI could handle USB2 speeds/devices, it seems like
one would *advertise* all ports served by the XHCI as "SS"
(which is not the case, here).
And, more specifically, that power supplied to the devices
in each class are handled independant of each other?-a (i.e.,
USB3 having more power delivery capability than USB2).
When USB3 was new then almost certainly a separate device but in the
latest generation of systems I honestly don't know.
Ditto.-a I'm not keen on taking things apart to find out.
Finally, is the power handling done with external (to the
controller) FETs or passed directly through (particularly on
the USB2 ports)?
On USB2 I suspect mostly they are pass through. USB3 can use higher
currents and voltages that may be done by an external FET.
SWMBO's legacy desktop has developed a power problem
with the USB2 ports (front and back).-a If power is passed
internal to the controller, then it's just not worth my time
to even open the case...
Might be easier to interpose a powered hub between the offending ports
and whatever you want to connect as a means of extending its life.
I thought of that but she's already got quite a collection of kit on her
desk and one more would just add to the confusion.-a <frown>
Taking Lasse's suggestion, I can see at least two EHCI and one XHCI.
There are 6 ports on the rear and 4 up front.-a So, likely the XHCI conductors are split and the two EHCIO handle separate clusters
of ports (front vs rear).
Her "problem" manifested in all of the USB2 ports which suggested
the *load* was more likely the problem (unless there was a seperate
LDO feeding just the USB controllers).-a USB3 ports had no problem.
OS did not throw an overcurrent warning (and shut down the port(s)).
Yet, I can see the LEDs on the keyboard blinking randomly -- as if
it was being plugged/unplugged rapidly (no OS announcement of this
but I don't think the OS announces keyboard/mice events?)
She had the mouse plugged into one of the two USB2 ports present on the keyboard (seems a logical choice).-a So, the ONE connection from the keyboard
was representing TWO devices/loads.
The absence of the overcurrent event suggests maybe the keyboard just couldn't handle the added load and *it* was misbehaving?-a An identical replacement keyboard exhibits the same problem.-a (though I didn't try
to replace the mouse at the same time-a <frown>)
Dunno.-a I rearranged her cables so each device had its own
port, keeping the front ports free for thumb drives, etc.
This *seems* to work -- I'm sure she'll let me know if it
acts up, again.-a <frown>-a (it is no fun being an IT department!)
I located an identical spare machine in my stash (actually, *two*!)
so if it continues acting up, I'll just pull the disk and give
her a "new" machine -- a lot easier than trying to install all her
legacy software on a different make/model machine, given MS's fussiness!
On 15/08/2026 15:18, Don Y wrote:
On "business class" PC's, is it safe to assume the USB2 ports
(front and back -- typically 4 or 5, total?) are handled by one
controller and the USB3 ports by another?
It probably depends on age and number of USB ports.
Some of mine have two USB controllers one for the set of four or six on the
back and one for the pair on the front panel.
There are a mixture of USB2 & USB3 ports in each location.
AFAIK, controllers are USB2 (EHCI) or USB3 (XHCI); while
the XHCI could handle USB2 speeds/devices, it seems like
one would *advertise* all ports served by the XHCI as "SS"
(which is not the case, here).
And, more specifically, that power supplied to the devices
in each class are handled independant of each other?-a (i.e.,
USB3 having more power delivery capability than USB2).
When USB3 was new then almost certainly a separate device but in the latest
generation of systems I honestly don't know.
Ditto.-a I'm not keen on taking things apart to find out.
Finally, is the power handling done with external (to the
controller) FETs or passed directly through (particularly on
the USB2 ports)?
On USB2 I suspect mostly they are pass through. USB3 can use higher currents
and voltages that may be done by an external FET.
SWMBO's legacy desktop has developed a power problem
with the USB2 ports (front and back).-a If power is passed
internal to the controller, then it's just not worth my time
to even open the case...
Might be easier to interpose a powered hub between the offending ports and >>> whatever you want to connect as a means of extending its life.
I thought of that but she's already got quite a collection of kit on her
desk and one more would just add to the confusion.-a <frown>
Taking Lasse's suggestion, I can see at least two EHCI and one XHCI.
There are 6 ports on the rear and 4 up front.-a So, likely the XHCI
conductors are split and the two EHCIO handle separate clusters
of ports (front vs rear).
Her "problem" manifested in all of the USB2 ports which suggested
the *load* was more likely the problem (unless there was a seperate
LDO feeding just the USB controllers).-a USB3 ports had no problem.
OS did not throw an overcurrent warning (and shut down the port(s)).
Yet, I can see the LEDs on the keyboard blinking randomly -- as if
it was being plugged/unplugged rapidly (no OS announcement of this
but I don't think the OS announces keyboard/mice events?)
She had the mouse plugged into one of the two USB2 ports present on the
keyboard (seems a logical choice).-a So, the ONE connection from the keyboard
was representing TWO devices/loads.
The absence of the overcurrent event suggests maybe the keyboard just
couldn't handle the added load and *it* was misbehaving?-a An identical
replacement keyboard exhibits the same problem.-a (though I didn't try
to replace the mouse at the same time-a <frown>)
Dunno.-a I rearranged her cables so each device had its own
port, keeping the front ports free for thumb drives, etc.
This *seems* to work -- I'm sure she'll let me know if it
acts up, again.-a <frown>-a (it is no fun being an IT department!)
I located an identical spare machine in my stash (actually, *two*!)
so if it continues acting up, I'll just pull the disk and give
her a "new" machine -- a lot easier than trying to install all her
legacy software on a different make/model machine, given MS's fussiness!
It might be worth buying a USB power meter.-a It avoids a lot of
guessing and costs very little.
Some of them have USB-A and USB-C ports which covers allNo BT on her computer. She already has a cordless mouse and keyboard
likely options.
To avoid unnecessary cables I like to use a Bluetooth wireless
mouse.-a Microsoft make some very cheap and reliable BT mice.
They communicate with the BT transceiver inside the PC so there
is no need for a USB dongle to communicate with the mouse.
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