Mac Pro 2019 Flash storage and data drive difference

OK, I bought my Mac Pro in 2020, I have another Mac Pro 2013 ( which is now my main computer)

Rather than open up the case on my 2019 I wanted to ask about the drives inside it.

I have a 2TB hard drive as the main SSD, then I see a 2TB Sata. I do not remember two internal drives in this machine so are the two drives actually ONE?

Then I also bought an external drive 8TB for back ups ( that I know about)

Any help here?