USB hubs can cause instability on your Mac


USB HUbApple has released a support article at http://support.apple.com/kb/TS3169 explaining how third-party usb hubs can cause instability on your Mac.

Symptoms

Some third-party USB hubs and devices connected though them may disconnect unexpectedly after the computer is woken from sleep. This may cause unexpected behaviors such as general system instability within open applications, or data loss if a connected device was being used to store data from an open document. If a printer was connected through the third-party USB hub, it may not be recognised.

Resolution

This behavior will only occur if the following conditions are met:

• The third-party USB hub doesn’t support the proper USB wakeup sequence.
• The third-party USB hub is connected downline to another USB hub. Note: Apple displays containing USB ports are considered to have a hub, so if you connect a third-party hub to the display, then that USB hub is considered downline.
• The computer is woken from an external USB device such as a mouse or keyboard.

The problem can be avoided by doing the following:

• Connect all USB input devices, such as mice and keyboards, directly to a USB port on the computer or to an Apple display that is connected directly to a USB port on the computer.
• Press the power button on the computer to wake it up instead of using an input device that is connected to a third-party USB hub.
• Connect USB storage devices directly to a USB port on the computer to prevent third-party USB hubs from affecting them.

Note: Wireless input devices that use the computer’s built-in Bluetooth interface will not cause this problem.

Note: Third-party developers may change the specifications of their products at will without notifying Apple, so we cannot provide a list of hubs that correctly or incorrectly support the USB wakeup sequence.

For more information on third-party product specifications and features, contact the manufacturer of the device.

Comment:

The biggest problem with Apple’s suggested solution is that most Mac laptops come with only a few usb ports and most users have several more devices than ports, so unless Macs start coming with a dozen or more usb ports users will have to resort to using usb hubs.

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