Well, easy to ask but somewhat hard to answer... I had almost the same question roughly 35 years ago. Here's what I suggest: Read The Design and Implementation of the Unix System V by Maurice Bach. Dive into the sources of Minix 1.5 (the first one leveraging protected mode) and read Tannenbaum's documentation on this OS (I guess that's what Linus did as well before he coded his first kernel...). Read the INTEL 80386 PROGRAMMER'S REFERENCE MANUAL 1986 to gain an understanding of how HW supports OS design ideas. Sure, these resources are old, but the basic concepts they tell about are still valid. While studying you will certainly encounter new questions, and grasping the answers (with help of Google) will lead you step-by-step into the present of OS design.

I used CUDA for parallelization of a Java program. The task was about accelerating a fairly simple algorithm for projecting bitmaps. It was fun and I made an [infographic](https://create.piktochart.com/output/25355418-java-parallelization-with-cuda) on my method. Found GPGPU quite exiting but lost it from sight, anyway... Regards, Jürgen.