'_'
In memory size for the signal.
Implemented in ADF::SignalImp< T >, ADF::SignalImp< Short_t >, ADF::SignalImp< UInt_t >, ADF::SignalImp< Float_t >, ADF::SignalImp< Double_t >, ADF::SignalImp< UShort_t >, and ADF::SignalImp< Int_t >.