External ports and connections on your Mac mini (Late 2014)
There are a total of four USB 3.0 ports. You can connect USB 3.0, USB 2.0, and USB 1.1 devices to these ports.
USB 3.0 (also known as "SuperSpeed USB") can transfer data up to 5Gbps. The power available to USB will lessen for each device you connect. For example, the last USB device will have the least power available to it, and it might need it's own power supply. Learn more about USB 3.0 on your Mac.