or  Rate  used  to  create  the  related  principal  balance  schedule.  Based  on  the  Modeling Assumptions, the initial Effective Ranges for the PAC and TAC Classes are as follows: Class Initial Effective Ranges PAC I Classes PA, PB and PC (in the aggregate)  .......................... 100% PSA through 250% PSA PAC II Classes CA .................................................................................... 130% PSA through 250% PSA PX .................................................................................... 132% PSA through 250% PSA TAC Classes OT and TX (in the aggregate)  ................................ 184% PSA through 240% PSA •   The principal payment stability of the PAC I Classes will be supported by the PAC II, TAC and Support Classes. •   The principal payment stability of the PX Class will be supported by the related Support Classes. •   The principal payment stability of the CA Class will be supported by the TAC and related Support Classes. •   The principal payment stability of the TAC Classes will be supported by the related Support Classes. If all of the Classes supporting a given Class are retired before the Class being supported is retired, the outstanding Class will no longer have an Effective Range and will become more sensitive to prepayments on the related Mortgage Loans. There is no assurance that the related Mortgage Loans will have the characteristics assumed in the Modeling Assumptions, which were used to determine the initial Effective Ranges. If the initial Effective Ranges were calculated using the actual characteristics of the related Mortgage Loans, the initial Effective Ranges could differ from those shown in the above tables. Therefore, even if the Mortgage Loans were to prepay at a constant rate within the initial Effective Range shown for any Class in the above tables, that Class could fail to receive Scheduled Payments. Moreover, the Mortgage Loans will not prepay at any constant rate. Non-constant prepay- ment  rates  can  cause  any  PAC  or  TAC  Class  not  to  receive  Scheduled  Payments,  even  if prepayment rates remain within the initial Effective Range, if any, for that Class. Further, the Effective  Range  for  any  PAC  or  TAC  Class  can  narrow,  shift  over  time  or  cease  to  exist depending on the actual characteristics of the related Mortgage Loans. If the related Mortgage Loans prepay at rates that are generally below the Effective Range for any PAC  or TAC Class, the amount available to pay principal on the Securities may be insufficient to produce Scheduled Payments on such related PAC or TAC Class, if any, and its Weighted Average Life may be extended, perhaps significantly. S-15