Efficient HeapNCanagementMinHthe Concrete ABC Machine John van Groningen, Eric Nocker, Sjaak Smetsers Abstract This paper gives a description of the heap management system used in the implementation of Concurrent Clean. The compilation of Concurrent Clean to concrete target machine code is done with the aid of the abstract ABC machine. The ABC machine is a stack based graph reduction machine. The way graphs can be represented and manipulated on a real machine efficiently will be discussed. An important part of the heap management system is formed by the garbage collection algorithm: a combination of a copying and a sliding compaction garbage collector. It will be shown that a smart node representation together with the proposed garbage collector makes it possible to run large functional programs on rather small machines.