I have always wondered why computers have two separate units for permanent data storage and temporary data access, as the time that it takes for data to be moved from permanent storage is one of the greatest delays in the functioning of modern computers, and has been for the two to three decades since their emergence.
With solid-state drives now becoming reliable and affordable, the delay between storage and memory has greatly decreased, but it seems to me that it would still be more efficient to have a single unit function as both permanent storage and temporary memory, which would allow for nearly-instantaneous access of the data that it contained.
Of course, I understand that the reason for which memory and storage are still handled by separate devices is that there is no inexpensive and efficient manner for developing a device that can perform both functions, but my questions concern a time when such a solution has been realized:
First, what numerical specifications shall be important when measuring the performance of a unit that functions as both memory and storage? I imagine that the important specifications would be the unit's storage capacity and its operating frequency/data transfer rate, which are also the important specifications for both current memory and storage devices, as well.
Second, what type of interface would such a unit use? I imagine that it would be either the PCI-express interface, or a new interface that combined PCIe with the current DRAM interface.
Third, when may such a technology become feasible, if ever? I certainly hope that that task can be accomplished in the near future.
What does everyone else say on this subject? I await your responses.