f FIG. 2; FIG. 8D is a schematic perspective view of a part of a base member of the shelf of FIG. 2; FIGS. 9A, 9B and 9C are schematic front, top and rear views, respectively, of an example of a midplane of the shelf of FIG. 2; FIG. 10 is a schematic cross section view through the shelf of FIG. 2; FIG. 11 is a functional block diagram of an example of an information processing subsystem for the in