I hadn't read about this before. From Wikipeida: <i>The software of the probe runs on Nucleus RTOS operating system. Nucleus RTOS is a real-time operating system (RTOS) offered by the Embedded Software Division of Mentor Graphics for various central processing unit (CPU) platforms. Nucleus RTOS is embedded software and is in an estimated 2.11 billion devices worldwide. ... The Nucleus RTOS is designed for deeply embedded systems applications including consumer electronics, set-top boxes, cellular phones, and other portable and handheld devices. For limited memory systems Nucleus RTOS can be scaled down to a memory footprint as small as 13 KB for both code and data.</i><p>2.11 billion devices world wide, and 1 device beyond Pluto. The most wide spread operating system developed by the humans of Earth.