From Earth to orbit with Linux and SpaceX | ZDNet
The Falcon 9's onboard operating system is a stripped-down Linux running on three ordinary dual-core x86 processors. The flight software itself runs separately on each processor and is written in C/C++. […] We don't know, however, what chips the Falcon 9 uses. Chances are, though, their design is at least a decade older than what you'd buy at a Best Buy now.