When I connect a USB mouse to a working system, it will work fine but serial mouse isn't recognized by the system? To get the serial mouse working, I need to restart the system. Why is this?
If I understand correctly, you want to know why USB connections don't need a reboot and serial connections do.
It might have changed, but as I recall, USB ports are always monitored, so if you add something, it automatically get recognized. Serial ports are only checked at boot time. So if there's nothing connected, then your PC won't try checking that port again.