You get to pick! In our cloud environment, you choose your hardware from any of the standard EC2 instances types. Changing your hardware is as easy as choosing from a menu, literally.
Unless you are using the "Free" tier, each of your Runs will get its own instance of whatever hardware type you choose, letting you use many machines at once.
Our On-Premise version installs on your network, so you can use whatever hardware you have available.