This object classifies the module as a single module, control timing module (ctm), I/O module (lm), or fabric/switching module (sm), as the description explains. An admin scanning the whole module table uses this field to programmatically separate the switching fabric and control-timing modules -- the ones everything else in the chassis depends on -- from ordinary line cards, without having to cross-reference model strings for every row. For example, a value of sm(4) flags the switch fabric module whose failure would affect every line card in the chassis, unlike a single lm(3) line card failure.