patentability

It depends. Usually you can expect the best results - to be patented - if the combination of the two components results in an unexpected or more efficient result, operation, use, function, or the like - in simple terms, the combination is greater than the mere sum of its parts. A good example of this is the original patent for a pencil with an eraser on its opposite, non-writing end - USP 0019783. The writing end of the pencil performs as intended, the eraser end of the pencil performs as intended, but the combination is uniquely useful in that an eraser separate from the pencil is no longer needed, is not readily lost or misplaced, and is always available to erase or change what one has written.
In short, a new, useful function for the overall combination - or, as I said, the combination is effectively greater than the mere sum of its parts.