A garbage collector divides the garbage-collected heap into "cards." It maintains a table containing a card-object table entry for each card. A card's entry contains information from which the collector can determine where any references in the card are located and thereby identify objects that may be reachable. Specifically, although each entry is smaller than a memory address, it has enough possible values to give the relative location of the object in which the associated card begins or to direct the collector to another entry for that information. But the entries are additionally grouped into sequences of contiguous entries that together are large enough to contain a complete address. When every card associated with a entry in a given (address-sized) entry sequence begins in the same object, that entry sequence is together given a value that the collector can recognize as indicating that object's absolute location.