A hotfix is available to address the USB transmission rate drop on Windows Vista-based and Windows Server 2008-based computers that are connected to some USB devices that have multiple USB endpoints
When you connect a Windows Vista-based or Windows Server 2008-based computer to some USB devices that have multiple USB endpoints, the transmission rate over the USB connection may decrease significantly.
The USB transmission rate partly depends on the number of USB endpoints that are connected to the USB controller. Therefore, for each endpoint that is connected to the USB controller, the USB transmission rate will decrease slightly. However, when this problem occurs, the USB transmission rate decreases significantly more than expected.
For more information on this issue, including potential causes, workarounds, and resolutions, see: Microsoft KB Article KB954052.