As of my last knowledge update in January 2022, the International Space Station (ISS) primarily used a combination of different operating systems for its various computer systems. The majority of the ISS's critical systems, including command and control functions, typically ran on custom-built redundant computers using a specialized real-time operating system called RTEMS (Real-Time Executive for Multiprocessor Systems).

However, the laptops used by astronauts for day-to-day tasks and scientific experiments often ran a variety of operating systems, including both Linux and Microsoft Windows. NASA has used both operating systems on the ISS, and the specific choice might depend on the requirements of a given task or experiment.

Keep in mind that information might have changed after my last update in January 2022, so it's advisable to check more recent sources for the current operating system configurations on the ISS.