Being a computer organizations and architecture expert One of the greatest challenge in learning one is how broad the literal computer science is. Just talking about memories and CPUs would just took you to endless adventure of this technology. How does the expert manage to understand all of this if I ever want to be one of them? 

Maybe someone ever be on my position, not just want to survive the exam but wanted to be the expert of this field especially on the hardware side and rarely ever grasp all the concepts.
Study and practice for years.  Years and years.
No one understands all of it.  Everyone specializes.
People get a broad sense of the field, but they don't learn all of it.  Then, they learn what they need to know, when they need to know, and only then.


So, keep at it.  You can understand enough to be effective, even if you don't know everything.