About HILS construction with Simulink Desktop Real-Time

I am currently trying to build HILS. So I found out that there was a function called Simulink Desktop Real-Time by searching, but it has not yet been handled.

The question is, I hear that RTOS (Real Time OS) is generally required when constructing HILS. However the explanation on the MATLAB homepage says "Prototyping on your computer or hardware in the loop Simulation. "

Please let me know if you can understand whether HILS can be built only with OS such as Windows / Mac, or if the necessity of RTOS will appear as in this sentence.

Also, I still don't understand the necessity of RTOS. I don't think it's a question here, but it would be helpful if you could tell me that.