What is the difference between simplex, half duplex and full duplex?

These are different forms of data transfer. Simplex means that data can only travel in one direction between an interface. An example of this would be a keyboard - you type into the computer which is registered in the CPU but the CPU doesn't send things back to the computer.Half Duplex means data can travel in both directions, but not at the same time. An excellent (and typically one of the only examples you'll come across) is walkie-talkie devices. You press the button and whilst it is held down, the other device can hear you but you wouldn't be able to hear any return transmission as long as you are transmitting data.Duplex means data can travel in both directions at the same time - this is easy as you use the internet all the time!