We study the out-of-equilibrium dynamics of several models exhibiting
ageing. We attempt to identify various types of ageing systems using a
phase space point of view. We introduce a trial classification, based
on the overlap between two replicas of a system, which evolve togethe
r until a certain waiting time, and are then totally decoupled. In thi
s way we investigate two types of systems, domain growth problems and
spin glasses, and we show that they behave differently.