https://www.zdnet.com/article/from-earth-to-orbit-with-linux-and-spacex/

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++.

The Dragon spacecraft also runs Linux with flight software written in C++. The ship's touchscreen interface is rendered using Chromium and JavaScript. If something were to go wrong with the interface, the astronauts have physical buttons to control the spacecraft.

 

My first job out of college was glass cockpit displays for a jetliner. Each LRU (black box) had 3 processors - 2 Z8000s and 1 x86. For attitude display the x86's primary purpose was to compute the same graphics commands as the Zilogs, and if there was any discrepancy, the display would go blank. The x86 was selected to add a layer of redundancy to protect against deficiencies of a single architecture.