Does having a better memory mean more storage “space” or better retrieval methods?

I’ve read that the human brain capacity has 2.5 petabytes worth of memory storage. I have an excellent memory for details; even super obscure things that happened decades ago. I only have an average IQ but my recall is very good especially when my memory is jogged or if I had read something more than 1 time. I read that people with Autism may have better memories; and it is possible I am on the spectrum due to my lack of social skills. I also have read that people with larger visual cortex’s have better memories as well. This would imply that part of the brain is bigger and has more “space”. Yet I have read that forgetting is due to retrieval problems and not the inability to store stuff. Yet their are also a handful of people who remember everything and that is not the norm by any stretch of the imagination. So what’s the verdict. Is my memory better because I have a thicker, larger brain matter with more space OR is the retrieval system in my brain wired better OR 
because I constantly “replay” memories in my mind because I have OCD. Is that helping strengthening the memory creating the illusion that I have a good memory?