Advances in performance are largely about impedance matching, from sequential access tapes to registers in a CPU. You want to use an efficient interface and abstraction for the level you're at. The direction of progress is toward faster, more randomly accessible with less seek cost: HDD -> SSD -> XPoint, etc. This totally makes sense--using RAM through a disk interface (e.g. RAM disk) is useful if you want a faster disk, to get something faster change the interface to take advantage of the medium.