Comment by torginus

FWIW, Windows is not a true RTOS, but it does get pretty darn close.

The true hallmarks of an RTOS kernel is hard-realtime scheduling usually with round-robin priorities, and support for priority inversion, which is when a low priority process blocks a high priority one, it inherits the high priority temporarily to meet the deadline.

Windows is threads have a priority, with the highest priority thread occupying the CPU - however there's a series of 'hacks' that allow it to emulate real time behavior.

Threads can get a priority boost in some cases, such as the aforementioned priority inversion case, when the user interacts with the program associated with the thread, when the thread hasn't run for a long time etc.

Additionally there's a set of 'real-time' priorities that can preempt all non-realtime priorities and you need admin or kernel access to set this prio level, as these threads will lock up your system because they can't be preempted.

While I wouldn't trust Windows to control an ICBM, but it's good enough at giving resources to user processes so the your UI feels responsive.