Oh yeah... did I mention that it has a USB hub in it? Why the hell are we still shipping PCs with 12-year-old PS/2 technology?Easy. Because USB is not a perfect replacement for PS/2 input devices.
- There is a large amount of latency on the USB bus as well as software latency incurred due to processing the USB packets. There is practically no wire latency with PS/2 and the protocol is dead simple to parse. You can create a little microcontroller project to interface almost any simple device to a PS/2 port. With USB, you need a separate ASIC to even begin to get anything done.
- USB controllers typically share interrupt levels with other PCI devices. On systems without an IO-APIC, this translates into increased software overhead on every interrupt, because the interrupt handler for every device sitting on that interrupt is invoked. Whereas with PS/2 devices, you have an IRQ reserved for the keyboard and an IRQ reserved for the mouse. Since they are edge triggered ISA interrupt lines, there is no possible way for them to be shared even if you wanted to. Therefore the correct interrupt handler (and ONLY the correct one) is invoked in response to a PS/2 event.
In short, there is no possible way on any but the fastest of current machines for a USB mouse to approximate the responsivity of a PS/2 port mouse being sampled at 200Hz (the maximum rate the port will tolerate).