 The original 1ESS packaging had all the ferrods of an LSF together, and separate from the line switches, while the later 1AESS had each ferrod at the front of the steel box containing its line switch.Odd numbered line equipment could not be made ground start, their ferrods being inaccessible.The computer controlled the magnetic latching relays by Signal Distributors (SD) packaged in the Universal Trunk frames, Junctor frames, or in Miscellaneous Trunk frames, according to which they were numbered as USD, JSD or MSD.