Abstract: A point of sale system having an active and a spare data processing system, each including separate read/write memories, with only one of the systems being active at a given time, but with the active system being able to selectively acquire data from the read/write memory of the spare system upon start-up and including means for verifying which read/write memory of the active or the spare system contains valid, most current data which is then transferred to whichever system is the active system, the read/write memories of each of the two systems having a built-in generation number counter which is incremented by one whenever either the data of the inactive read/write memory is caused to be transferred to the active read/write memory or whenever the counts in the generation number counters of both read/write memories are equal, this change in the generation number counters taking place only at the start-up of the system.