I've made an attempt recently to understand how USB works inside of my laptop. My laptop is X61T from Lenovo and it has 3 USB ports on the back of the chassis. Intel documentation states that the southbridge in my laptop supports up to 10 USB ports. Each of those ports is both USB 1.0 or 2.0 compatible (the router logic inside the chip decides, whether the device should be connected to the UHCI or to the EHCI host controller interface). Here is how it looks in Device Manager under Windows XP:
The ICH8 chipset supports up to 10 USB ports. Two of those ports are already used internally, by the fingerprint reader and by the Bluetooth module.
This means that eight ports are still available.
The question is: why does Windows XP list all of the ports available, when I may only use 3 of them max at any given time? (bc my laptop has only 3 external USB ports).
I understand that there are actually 20 'virtual' USB ports available (10 of them being USB 1.0 and 10 of them being USB 2.0) and that each pair of a 'virtual' USB 1.0/2.0 ports is binded to one physical USB port on the laptop's chasis (so if I plug in an USB device to a physical USB port, either the virtual USB 2.0 port or the virtual USB 1.0 port will be used). So i.e. if I have 3 USB 1.0 devices connected to physical USB ports, 3 USB 1.1 'virtual' ports will be occupied and if I have 3 USB 2.0 devices connected, I will have 3 USB 2.0 'virtual' ports occupied. This is still only 3 ports and not the remaining eight that should be available.
The related question would be: could I make those additional ports available by soldering wires to the southbridge pins?