From your reply, I gather that you would like to know if there is any difference in performance when the mouse is plugged to the USB and the PS/2 ports.
Let me assure you that in most cases, there would not be a performance difference. In the former, the mouse works as a USB mouse and in the latter the mouse is recognized as a PS/2 mouse.
However when the mouse is used on a Laptop, it is recommended that the mouse be plugged to the USB ports. The reason that is that, when the mouse uses the PS/2 port then there might be conflicts with internal pointing devices on the Laptop; as they also use the PS/2 bus for communication.
I hope this information helps. Please feel free to write back in case you need additional clarifications on this issue. It will be my pleasure to be of assistance.
Thank you for using Logitech's Electronic Technical Support. My name is Rohit. The following information addresses your original question. You may wish to print this out and/or save this on your computer.
We would like to inform you that if when you plug in your mouse in the USB port the Windows OS will automatically detect the mouse and you can start using it. If you plug in your mouse in a PS2 port the Windows OS will not detect the mouse. For the Windows OS to detect your mouse you will have to restart your computer.
The performance of the mouse will be the same whether you use it on a PS2 port or USB port.
If you have additional technical questions regarding this issue, please reply to this email.
If you have questions regarding another issue with your product, or questions regarding another product, please visit our web site at www.logitech.com and submit your question.