USB 3.0 is compatible with older versions of the USB standard it?

Yes. Plug a USB 2.0 device will be able to insert a USB 3.0 slot and a good job. Similarly, a standard USB 3.0 devices can plug into a standard rub a USB 2.0 slot, use a USB 2.0 speeds. However, other than the USB 3.0 connector USB 2.0 slots to be fast, so the old version of the slot and can not be used normally.