Combining card marking with remembered sets: How to save scanning time

We consider the combination of card marking with remembered sets for genera tional garbage collection as suggested by Hosking and Hudson [3]. When more than two generations are used, a naive implementation may cause excessive and wasteful scanning of the cards and thus increase the collection time. W e offer a simple data structure and a corresponding algorithm to keep track of which cards need be scanned for which generation. We then extend these ideas for the Train Algorithm of [4]. Here, the solution is more involved, and allows tracking of which card should be scanned for which car collectio n in the train.