Newbie here:

I will want/need to create an array of approximately 300K rows and 20
columns. The array will be an array of either 32-bit quantities or 64-bit quantities.

Does Ruby support native 64-bit quantities?

What's a good/best way to to create such an array. Is there a way to
tell Ruby, "OK, I'm done with this array."

Can one create such an array such that the garbage collector can
free the memory in one fast operation?

Ralph