His series on YouTube, Dave's Garage, has really helped me to conceptualize Operating Systems in the past that I used, but didn't really fully understand. I started with Atari DOS, but moved to the 286 roughly around the time it started to become popular, along with MS-DOS. I'm 45 now, so didn't think about things as deeply back then, as far as constraints and why things may have been built the way they were. I think his series really does a great job at looking into both technology and company politics (especially his time at Microsoft).
https://youtu.be/xi1Lq79mLeE?feature=shared