Isn't that more or less what all abstraction is about, getting an interface that allows you to work with the "what" but not the "how". When I call file open, I

Isn't that more or less what all abstraction is about, getting an interface that allows you to work with the "what" but not the "how". When I call file open, I get the "what", a file to work with, but not the "how", DMA access, Spinning rust, SSDs, could be an NFS in there who knows. Yes, the "hows" have impacts on performance. When implementing or selecting the "how" those performance criteria flow down into "how" requirements. As far as I am concerned that is no difference from correctness requirements placed on the "how". Coming from the other direction. If I am hard disk manufacturer I don't care about the "what". I only care about the "how" of getting storage and the disk IO interface implemented so that my disk is usable by the file system abstraction that the "what" cares about. I may not know the exact performance criteria for your "what", but more performance equals more "whats" satisfied and willing to use my how.