An apparatus is described. The apparatus includes a package on package structure. The package on package structure includes an upper package and a lower package. One of the packages contain memory devices of a first type and the other of the packages contain memory devices of a second type. I/O connections on the underside of the upper package's substrate are vertically aligned with their corresponding, first I/O connections on the underside of the lower package's substrate. The first I/O connections are located outside second I/O connections on the underside of the lower package's substrate for the lower package.