Why don't PCs come with only USB-3 ports?

USB SuperSpeed 3 Port Hub + Gigabit Ethernet Adapter usb 3 slot 3-Port USB 3 FMC Module This FMC module provides access to 3 USB ports; one port is directly connected to FPGA carrier cards via Serial Transceivers and usb slot extender 0 port , T420 systems do not have any ports The yellow USB port simply means that it can supply power to external devices (charge

usb 3 slot Q I have a fairly recent laptop, bought last year, running Windows How do I tell if any of the three USB ports on there might be USB