Memory mapped files can be created using access=‘stream’, which gives byte addressing.
But why have the data in a file ?
Create a derived type structure with allocatable components and then most file data structures can be replicated in memory.
Just buy enough memory for the project. Now it is a very big database that can’t fit into memory.
Now with OpenMP, the strategy is managing cache, so memory is used for data structures as disk files once were. Data structures can also be more flexible as the analysis proceeds and data components can be re-allocated.