Programmable Real-time Units (PRUs) are fast (200-MHz, 32-bit) processors with single-cycle I/O access to a number of pins, and full access to the internal memory and peripherals on the AM3358 processor on BeagleBones. They are designed to provide software-defined peripherals as part of the Programmable Real-time Unit Industrial Control SubSystem (PRU-ICSS), and are capable of implementing things like twenty-five pulse-width modulators, four soft UARTs, and stepper motor drivers. Having these controllers integrated is really handy to avoid throwing in another device to control or interface to a new peripheral. The real power comes when high bandwidth is needed between the main CPU and these controllers, such as in BeagleLogic.net, MachineKit, or LEDscape. Also, all these real time control of inputs and outputs are done while running a full Linux OS on the AM3358 processor, which is very compact.